The Dursleys where sleeping on Harry Potter's birthday when someone crashed truth the door, was a very, very tall man. The man asked for Harry. Harry was very afraid.
Hagrid starts saying about Hogwarts a school for wizards and witches, when Harry heard that he think that Hagrid was crazy, after a long time Hagrid say to Harry that he knew his parents, when Harry heard that he started asking a lot of questions to Hagrid.
After Hagrid answer all the questions he says that harry's parents was a wizard so Harry is a wizard too, in the first time Harry don't believe, the time has passed and Harry started to believe in Hagrid.
Some time later Hagrid invited Harry to study at Hogwarts, a few minutes later Harry accepted the proposal, but the Dursley's don't wana that Harry finds out he was a wizard or him to go to Hogwarts.
But Hagrid didn't like the Dursleys so he tell to Harry about how he got that scar, and how his parents had died, the truth is, there was a dark wizard named Vol... Vol... Voldmort and he had killed Harry´s parents. Voldmort tried to kill Harry but failed.
So a long time has passed and the Dursley let Harry go to Hogwarts, before they go to Hogwarts Hagrid says to Harry that need to pass in a other place first. Knowing how curious Harry was, he asked Hagrid where we were going, and Hagrid replied: To Diagon Alley.