Getting Started

Nuclear Tech is a big mod - after 9 years of development and counting, it has amassed a ton of content. Getting a good grasp on just how things work might not be easy at first, but fret not, this is why this guide exists.

Preamble

The Nuclear Tech Mod has many, many recipes, it's unlikely that any one person can memorize them all. While there are plenty of mods that aid you in that regard, only Not Enough Items will show you all recipes, including ones that make use of modded machines. Using NEI is crucial, and so is understanding how it works. Here are a few tips that might make your life a whole lot easier:

The NEI overlay can be toggled by pressing 'O' while looking at your inventory
On the bottom left corner of your inventory, given that the overlay is enabled, there is a button for an options menu. It is advised that you turn on the "Highlight Tooltips" option in the "World" category, as it will display the name of whatever block you are currently aiming at on screen. Alternatively, there is a NEI addon called "WAILA" which has the same core functionality, plus some extras.
Pressing R on an item will show you how it's made. In addition, pressing U allows you to see all the recipes it is used in.
When looking at recipes, you might not always see what you want to at first glance. If multiple pages are available, on the bottom there's buttons to go through pages of the crafting machine you're looking at (e.g. if you're looking at a workbench recipe, the bottom arrow buttons will lead you to more recipes of the workbench). The top arrow buttons, if available, will lead you to recipes in other machines (e.g. if you're looking at a workbench recipe, the top arrows will lead you to recipes of other machines, for example the furnace). This is very important, since some items can be made in multiple machines, and the machine that comes up first might not be available to you at the moment.

Things to do before you start

One thing that you can do before engaging in the progression, as well as something you should always do if you have the time, is looting structures. Your world is littered with buildings and dungeons alike, all full of stuff free for the taking. You shouldn't solely rely on structures for your resources, but they give you a head-start when it comes to progressing through the mod. Here's a list of structures which are great for raiding in early-game:

Antennas: A common structure with a few resources, mainly steel ingots, wires and basic circuits.
Radio stations: A great source of concrete and steel, the small side building also has tanks filled with diesel. The chests often also contain revolvers and sometimes weaker shotguns which are fantastic alternatives to your stinky old vanilla bow.
Relay stations: Huge antenna-like structures with loads and loads of steel. Steel sets are only marginally better than iron - but with steel so easily accessible and in such quantities, you'll be able to make steel tools quickly.
Crashed space ships: Somewhat rare and filled with items that aren't very useful in early game, they still contain a considerable amount of steel and a chest full of rare items, more often than not consumables and rocket launchers.
Crashed vertibirds: Helicopters that are buried in the desert, they are a good source of steel and often contain parts for power armor.
Factories: Large brick structures that contain machines and chests full of raw materials. There are explosive barrels the can be harvested and used to fuel diesel generators. Some say there's a treasure hidden in the lava.

However, this world isn't a place filled with just candy and free stuff, there's also places which you absolutely should not enter, or even approach, unless you are well equipped:

Nuclear power plants: Easily recognizable by their large cooling towers and by the fact that everything in proximity to it is dead, these structures contain many valuable resources. However, every power plant also has its own on-site nuclear waste storage, which causes ambient radiation levels to skyrocket. Unprotected players may die within less than a minute if they choose to approach a power plant. To add insult to injury, high levels of radiation can also turn creepers into mutated nuclear creepers, may Lauren have mercy on your soul if you encounter one of these.
Radiation hotspots: Rare, but extremely dangerous craters filled with rocks that are boiling from radiation. They offer no noteworthy loot, so it's best to avoid them.
Nuclear waste storage tanks: Tower-like structures with nuclear waste leaking out of them. Buried deep within all the nuclear waste usually lies a treasure chest, but without the equipment, you are unlikely to even get to see any of it without dying a dozen times.
Duds: Not very dangerous per se, but you should not meddle with them. There are certain ways to extract resources from them, but those are very dangerous and not relevant to you unless you have reached end-game.
Poison geyser: Easily recognizable from the lack of grass surrounding a patch of crumbled rock, the geyser periodically spits out a jet of poison gas. Below it there are a few blocks of yellowcake, although these aren't very useful until you have reached the nuclear age.
Missile Silos: Quite rare, and contain some of the most destructive weaponry available in the mod, and defended by old turrets that don't seem to ever run out of ammo. Once you have some good gear and some rare launch codes, you may find yourself venturing to one of these, but be careful.

Shopping List

The first few machines will need quite a stockpile of basic materials, so make sure you have a source of each before you settle on a base location:

Large quantities of iron, copper, and redstone.
Small quantities of industrial metals like aluminum, titanium, and lead.
Burnables like coal or charcoal.
Structural blocks like clay and sand. (for glass and bricks).
Hemp (for string), sugarcane, saplings, and dandelions.

Make sure to keep some raw aluminum ore for later, because you'll need it for firebricks. You can also obtain a good quantity of raw metal looting structures, as well as some circuits for later.

Okay, now where to start?

No matter what your end goal is, the very beginning of the tech tree always looks the same. You need to get these three things:

A machine template folder, made from paper and any dye.
A burner press, which is made from iron, a piston and a furnace
A special anvil, made from either iron or lead.

In addition, you may want some utility machines, like an iron furnace and a bricked furnace

Anvils

You will need an NTM anvil to progress, as they're used to create important machinery and items. They come in many Tiers, distinguished by the metal they're made from. You only need an iron or lead one for now. They're made with a block and six ingots of the respective metal. You'll be able to manually make plates with them later on, but that's not important right now.

The Machine Template Folder and You

Congratulations, the moment you have crafted the folder is the moment you have found your new best friend. This handy item will follow you through the entire mod, no matter how big or small the task, it will be by your side. The main functionality is to create templates for the assembly machine and chemical plant, siren tracks, fluid identifiers and press stamps. But one step at a time, in the beginning we're only interested in the latter one, which brings us to our next piece:

The Burner Press

The burner press uses fuel and a stamp to process metal. Stamps have limited durability, and will need to be replaced occasionally.

Flat stamps can be crafted with a desired material and some bricks. For the other stamp shapes, open the template folder and select the plate stamp option for your chosen material, and it will convert a flat stamp into the chosen variant.

Once you have a plate stamp, put the stamp in the top slot of the press and some copper at the bottom, and now the magic starts: You have made yourself your very own copper plates.

The burner press speed depends on its temperature, starting off quite slow and only becoming reasonably swift after a few seconds of use. Because the machine takes a lengthy time to heat up when running, it is recommended to process in batches. Don't worry about fuel efficiency, fuel is measured in completed crafting operations, not time taken.

If the time taken to warm up seems excessive, then I have some good news! You can craft a burner press preheater with copper plates, lava, and tungsten. When placed underneath the burner press, the preheater reduces the time needed to warm up, making the machine much more effective for small batches.

Metallurgy 101

Even if you have a stack or two of steel from looting, you are going to need far more to make progress in the mod.

I hope you stockpiled some clay and aluminum ore, because you'll need both to start making alloys. Craft your clay and aluminum ore into fireclay and start roasting.

The bricked furnace will be helpful here, because it gets a speed boost when smelting construction materials like stone or bricks.

Armed with copper plates and firebricks, you can now craft your second machine, the Blast Furnace. This machine has many recipes, but for now you'll only need the two most important ones: Steel and Minecraft grade copper (also known as red copper).

The blast furnace can be powered with coal or lava, which fills an internal buffer so that nothing is lost while the furnace is idling.

Eventually you are going to need many alloys, but these three are the most important ones:

Steel: an iron ingot and a lump of coal make one ingot of steel
Red copper: "industrial grade" copper and some redstone make two ingots of "mingrade" copper (mingrade is a shorthand for minecraft grade)
Advanced Alloy: mingrade copper and steel can be alloyed together to make advanced alloy.

Steel can additionally be made by directly smelting iron ore with flux, yielding 3 full ingots per ore!

Many of the recipes are additive, meaning you'll get 2 ingots from alloying. With this in mind, you should start using Advanced Alloy for your tools. Far more resource efficient!

After you get your first steel ingots, you can craft a blast furnace extension. The extension provides a dramatic increase in speed when placed on top of the blast furnace, so it comes highly recommended. Even with the extension, the blast furnace is still slow, so it would be a good idea to make multiple. Fuel consumption is accelerated as well, so the efficiency remains the same.

The Road to Automation

Soon it'll be time for your next machine, but you're not quite there yet. You'll need one more stamp: A wire stamp. Using your newly made red copper and some Tungsten, you'll have to make wires out of them. Tungsten wires, glass pane and an insulator make a vacuum tube! Once you have a sizable amount of red copper wires, you can craft motors, which, combined with the vacuum tubes and some metal blocks, make an assembly machine!

Assembly!

The assembler is the most important machine you'll make. Almost all other machines or items are made using the assembly machine. The interface might seem a bit confusing at first, but don't worry, it's simple. At first, the assembler must know what it's supposed to make. Many recipes make use of the same base ingredients, so there has to be a way for it to know whether it should make, for example copper plates or copper wires. Luckily, we have our template folder for just that: Get some paper and dye in your inventory, open the folder and look for the shredder (it's a small dark gray machine with a red top). Click on it, and it should give you the required template. Putting the template into the template-shaped slot will make the small red !-indicator disappear (which, when hovered over, should inform you about a template being required). Hovering over the template, or by using NEI, you can check which items are required to make the shredder. Gather them, put them into the assembler and...!

Nothing. The assembler needs electrical power in order to work. To produce this power, there are two machines available to you in the early game: The Wood-Burning Generator, and the Stirling Engine. The simplest to operate is the Wood-Burning Generator. Craft one in a crafting table and place it down next to the assembler so that the wires on the sides of the assembler connect to the dark ports on the generator, or use some red copper cables to connect them together. The Stirling Engine is operated with a "TU" generating machine placed directly under it, such as the Firebox, Heating Oven, Fluid Burner, etc. (Note: if you haven't made a crucible yet, this would be your first introduction to heat-based machinery.) Use an Anvil to create the Stirling Engine and your choice of heater, then connect your chosen generator to the Assembler. Now witness the might of the crafting automaton, creating advanced machinery in mere seconds!

Shredding like there's no tomorrow

The Shredder is not only required to progress with all the machines, it's also an incredible handy utility machine: Once powered up and equipped with shredder blades, it will crush ores into two piles of dust each, effectively doubling the yield! If you haven't already smelted all your ores, it might be a good idea to toss them into the shredder instead. It can also remove unwanted items such as dirt or half broken tools and turn them into scrap which you can use as furnace fuel. For the next step, you will need quartz, so get ready to go to the nether.

The Hell Zone

The nether has not changed significantly since installing Nuclear Tech, aside from two things:

There's now a couple of ores spawning in the nether, most notably uranium, tungsten and sulfur, all of which are also found in the overworld
The nether in its entirety is now slightly radioactive

The last fact might frighten you, but be assured it's just a mild 0.1 RAD/s which isn't all that big of a deal. It would take almost 3 hours for you to die in the nether from radiation, so take your time and get some quartz. Might as well use some phosphorous, but watch out for the white ingots - they'll set you on fire if you don't have a suit to protect yourself from them. There's also plenty of uranium which becomes interesting later.

Circuits Galore

Using cast steel plates, copper coils, tungsten bolts, and some more vacuum tubes, you can create your personal soldering station! With it, you can now craft many types of circuits using (mostly) basic parts. The first (and only for now) circuit you can craft, is the analog circuit board. Using some more vacuum tubes, a few capacitors, lead wires, and some printed circuit boards (PCBs), you can create the analog circuit board! Now that you have the power of soldering in your hand, you can create the chemical plant and unlock the power of chemistry. From here on out, it's your choice on how to go, although oil refinement is the direct next step to progression.