What qualifications would I need (as an American) to go to an English university?

I've read the qualifications needed to get into the University of Leeds as a UK student, however I don't understand how this translate into the American school system. I have decent grades (A's and B's) but no honors cles. I heard you needed three AP cles just to apply? Can someone please help me! Also, what else would look good on an application for an overseas student?