Resistors do basically what it sounds like they do! Resistors Resist the amount of current flowing through a circuit. (a circuit is a path of electricity. Basically if you connected a battery to a light you would have one of the simplest circuits possible)
So for example if you made the above circuit by connecting a battery to a light and then added a resistor anywhere in the circuit the light would be less bright than it was before. The amount of resistance in a circuit depends on how much resistance the resistor(s) have. Think of it as a river! the water flowing through the river is the current flowing through the circuit, the larger rocks in the river slow down the water (as the resistors lessen the current). Resistors will look like the resistor in the picture below, they usually will not be any other shape, they slightly vary in size and they will sometimes vary in color other than the creamy color like the one below, I have also posted a picture of a blue one so that you can see what I mean when I say they might vary in color other than the creamy color one below. So now that you know what they look like, you will hopefully not mistake them for anything else!
For windows (not sure if it will work for macintosh or other operating systems)
it is So much easier just use this program to read your resistors: www.mitmaro.ca/oldsite/files/rr.zip
note: this program will not give you any viruses. All you need to do to use it is click on the link above and then click SAVE and save it to your desktop or somewhere else that you will remember it. Once it is saved, click open. Once you have opened it Double-click on resistor reader and then click extract all, then click next, next again, make sure you have selected the checkbox that says "Show extracted files" Click Finish and then a window will pop up with some files double-click on resistor reader! now I will tell you how to use it: (do this when you need to have your resistors read)place the resistor down on your computer desk facing your computer. Place it so the gold band is facing the right side of your screen. Count the number of bands on the resistor. If it is four bands then under resistor type, select four band, if it is five bands select five band. now, start from left to right select the color on the left matching the color on the left of the resistor and so on the band on the right will usually be silver of gold. It is pretty straight foreward I guess.
Now for macs and other systems!
There is this website www.pealefamily.net/tech/resistor/
It only does four bands though I think that is probably all you will be dealing with though. But you need to read the above step for windows users because the one you will be using will be much the same. *READ ABOVE STEP!
So thats step 1!
Oh and one last note: you can combine resistors to make one resistor like lets say you need 22 ohm resistor, you can combine two 11 ohm resistors. and resistors are not directional, so you can put them either way around in the circuit!