In the schematic shown by Mike, the item labeled photo transistor is commonly known as a Light Dependent Resistor (LDR), as its name implies, it's resistance varies with the amount of light falling on it. With all due respect Jeff. and whilst not wanting to dampen your enthusiasm I have to tell you that you really are out of your depth here. Why not decide on what you really want to do and study that one subject until you thoroughly understand that subject before going on to something else.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus