The reason that Ron, and all the other people in the wizarding world, know all about Harry Potter is that Harry is famous, without even knowing it himself. The reason why he was left on the doorstep of his aunt and uncle is that both his parents are dead. They were murdered by an evil wizard who calls himself "Lord Voldemort". He is so evil that people are even afraid to say his name. Harry is famous because he survived the magical attack of the "He who must not be named", and since that day, Voldemort has gone into hiding.