Input/Output Gate:  What it says on the tin. It is a lever, that when you flick it, gives a current on the green wire.
NOT Gate (Inverter):  It does the opposite of Input/Output. When you flick the lever on, it goes off, and off, it goes on. This is more useful with buttons, (Example a piston door).
AND Gate:  You have to turn both levers on to get it to work. One or neither won't do it.
OR Gate: Press either lever (Or both) turns it on.
XOR Gate: I don't even... 
*I will finish this after school. Feel free to edit this*