I used the BBC bite size website when i was revising. But I am not sure if this fits with all exma boards so you are better off asking your teacher. The notes you make in class should be extremely helpful. I always look at past papers as well to see how the questions are worded.
Bite-size is good for things like that. However you have to be careful, as Vera said, about using websites you just happen to find, or are called wikipedia. Because noone controls what is on these websites they may not be correct.
I would reccomend on of the revision books you can buy, for whichever exam board you will be on. I used these a lot for my revision. There is the advantage I can write on them!