If you're going to be playing with microprocessors and the like, chances are you'll be doing a lot of soldering. I wish I'd known all this before I wasted hours fixing my mistakes. You'll make your own, but hopefully you won't be repeating mine.
First, make sure you have the appropriate tools.
You can buy a starter $100 kit from adafruit, here
The absolute minimum you need is this:
1) You need electronics solder. None of the heavy, thick stuff. You'll want the thin solder, and you'll want to buy half a pound at a time, at least.
60/40 Lead Solder, rosin core .031” - 1 pound for eleven bucks.
2) You'll need a soldering iron. Don't use coldheat! They look cool, but the tips break easily and are extremely expensive (10 bucks per little tip!!), the solder doesn't get hot enough, and you might fry your components because the coldheat device uses electricity to heat up the solder.
You'll want a flathead or conical tip. Make sure the point is as sharp as possible! You'll need it for when you have to get into the small spaces.
A basic radioshack model may work just fine.
A better model can be found here:
Feel free to buy one of each tip as well, if you want to spend the extra $13.
3) Cutters. I used basic diagonal cutters and they worked fine for me. You might want shear cutters. Whatever you find works best, go for it.
4) A desoldering tool. This is for when you make mistakes. Incredibly easy to use - push the shaft down, position the intake near your hot solder, click the button. The solder gets sucked in and hits the metal pole, where it instantly cools and hardens. Push the shaft all the way down to remove the collected hardened solder occasionally. If you want it can be reused but I'd recommend not reusing used solder.
They cost less than $3.
A more in-depth list can be found here
Now, on to the basic soldering guidelines.
PCB - printed circuit board
Lead - the thin metal stick attached to either side of your component.
IC - integrated circuit - this is the chip
Most of your basic projects will be soldering basic components on a through-hole printed circuit board (PCB).
Step 1: Put the component where it belongs so that the leads are sticking all the way through. Pay attention to direction (important with LEDs, electrolytic capacitors - the big circular ones, and diodes, among others; not important for ceramic capacitors, inductors, resistors). Generally the components that must be put in a certain direction will be asymmetrical in shape or painted differently on either end, or the leads will be different lengths.
Step 2: Bend the leads outwards so the leads are almost flat against the board. This ensures that the component does not fall out when you flip the PCB upside-down.
Step 3: Touch the soldering iron simultaneously to the lead and the PCB. You should be touching a small copper ring that the lead is poking through. Generally a second or two is enough for this to get hot. I usually only wait a second before I move on to
Step 4: Bring the solder and touch the tip to the lead and the PCB. You may or may not be touching the iron itself. Either way, it should start to melt almost instantly. Now, your hand that is holding the solder shouldn't move - the tip of the solder will melt off leaving the rest of the solder instact. The part that melts off should create a shiny bead that will fill in the hole between the PCB and the lead. Once this happens, remove the soldering iron. It should look like this:
See how the circled joint isn't shiny, and everything else is? That's a cold joint. All the other joints are shiny and good. If you get a joint that isn't shiny, touch the iron to it until it flows freely and fills up the hole and shines.
Step 5: Remove any extra with the desoldering pump.
Try to keep the heat on for as little a time as possible for electrolytic capacitors.
Also, when your project has chips, make sure you're using chip holders like these:
IC holder (IC = integrated circuit)
ICs (the actual chips)
So when you use a holder, you're avoiding the risk of burning the IC with your iron, and if the IC dies you just pop it out and pop another in without having to solder anything.
So this was the basic tutorial. For more in-depth guides, search the web or check out ladyada.net projects.