Pickup a book on simple electronics, a soldering iron, 60/40 solder (a little goes a long ways, don't get lead free solder), some small wire, probably 16/18/20 gauge, and practice soldering wire together. Research DC circuits, and LEDS.
Every LED is different, lets say you have 3 LEDS, that use 20ma, and 3.3v, a single 110ohm resistor, and those 3 LEDS in series will work on a 12v power source, if you get the resistor wrong, or use too much voltage you WILL blow the circuit out, and cause the leds to possibly pop upen.
As with an LED a capacitor is going to always be different, on voltage and capacitance. Capacitance is the amount of charge the capacitor is rated for. You also have different QUALITY capacitors. They are meant to provide CLEAN power to a circuit, kind of acting like a filter. Lets say you have a 16v circuit, but it fluctuates a little, and you need the voltage and current to be as stable as possible, the capacitor will "absorb" the extra charge, and save it for when the voltage/amperage drops below what is required. So you would use a 16-18v capacitor, with a specific capacitance to maintain that circuit.
A transistor is basically a light switch, you have some simple 3 legged transistors, and some rather... complicated ones. You have a Base, an Emitter, and I forgot what the third one is called. You won't really get into these till you learn a decent bit about DC circuits.
