Note: I am by no means an expert, but I consider my knowledge (and the knowledge of the instructables community at large) sufficient enough to educate those who wish to be educated.
Step 1: Resistors
To find the resistance of the four-band resistor:
look at the resistor, make sure the side that has a silver or gold is to the right (there might not be a band with one of these colors, make sure the side that has no band is to the right).
now you simply read it.
write down the first value
write down the second value
the third number tells you how many 0's to add to the number
the fourth number tells you the tolerance.
In the picture the resistor is red green red gold, so that would be 2500-5%. This means that it is 2500 Ohm's and has a tolerance of 5%.
Step 2: Diodes
Luckily, manufacturing companies make this easy on us. One side of the diode has a stripe on it. Electrons (electricity) flow from the cathode to the anode. The side with the stripe on it is the cathode.
Note: LED's (Light Emitting Diodes) are diodes, and therefore can burn out if inserted wrong.
If you build a circuit with Diodes, and you see smoke or flames coming out of it, DISCONNECT IT AS FAST AS YOU CAN more than likely you have inserted it wrong. It is ok if there is heat though, as long as there is not smoke or flame.
Step 3: Capacitors
There are two types of capacitors: electrolytic and ceramic.
Capacitors are measured in Farads.
Step 4: Transistors
There are three leads on a transistor, labeled "B," "E," and "C." These stand for "Base," "Emitter," and "Collector."
If there is no current flowing to the base, the transistor won't let the emitter and collector receive any current.
There are several types of transistors, two of them are NPN and PNP. "N" stands for negative, and "P" stands for positive. NPN means that the outer two leads are negative and the inner lead is positive. PNP means the exact opposite.
Step 5: Motors
With DC motors, the motor spins spins towards the negative energy.
Motors can also be generators, which is how your house is powered by AC.
Step 6: Speakers.
It is important to note that the only difference between a speaker and a microphone is that a microphone is a speaker specifically wired for input.
Step 7: Transformers
Transformers are used to change the voltage in a circuit. They can increase it or decrease it. A step-up transformer increases the voltage, a great example is the Tesla coil, which takes a voltage (usually 120V) and makes it MUCH bigger. An example of the opposite type of transformer would be a wall adaptor, which takes 120V (depending on where you live) and brings it down to something that won't blow your electronic joy up.
The number of wrapping on the coils is directly proportional the voltage in vs. voltage out.
Note: transformers can have four or five pins, on a four pin transformer, those are: +in, +out, -in, -out.
EDIT: 1/14/2011 thanks to frozenveinz, I now have a good picture of a transformer.
Step 8: Miscelleny
I will post abbreviations on this page. If there are any I forgot, please inform me.
IC= integrated circuit.
MOSFET=Metal Oxide Semiconductor Field Effect Transistor
LCD=liquid crystal display (basically a screen)
LASER= Light Amplification by Stimulated Emition of Radiation
Please post a link to any 'ible you make from this, including your very own death ray :)