Could somebody tell me sites gud enough for e-studies?

ya i want to do some studies now . I am bored with social networking. and now i want to do something good for me .could you please suggest me some websites which can help me in academics as well as to crack competitve exams. specially for mathematics and science and ya english too. this would be really helpful. And ya i am in 9 class but plz dont consider it much. thanx .Facebook friends if u view this plz help.