I'll give a simple but not quite complete answer. But since your question is pretty basic, I'll assume you're not asking for too much techeeze.
Electricity flows from the hot wire (usually black or red, although it can be lots of colors) through the lightbulb (or toaster or computer) and into the neutral wire (white or grey).
The hot and neutral wires are what are supposed to be used to carry electricy. If something goes bad, there is a ground wire to give the electricity a safe path to...ground or back to the electrical panel.
Normally, if everything's working fine. The ground wire doesn't carry any current. Ground is typically bare or green.
But the ground and neutral wires are tied together at some point back at the service entrance equipment and at the street. This keeps the neutral wire in your house and your neighbors houses at the same voltage (That is zero volts) So the neutral wire is refered to as the grounded wire but not the ground wire.
Now there are lots of times where you use two hots and no neutral (Anything that's 220Volts at home) or even three hots (but probably not in your house). And lots of other exceptions. Blah blah...don't sue me...blah blah...disclaimer...blah blah...hire an electrician...etc.
