The story
Harry Potter has grown up believing he is an ordinary boy with an unusually miserable home life. On his eleventh birthday he learns that the world is much larger than he was told: his parents were wizards, he has a place at Hogwarts School of Witchcraft and Wizardry, and his own name is already known throughout the magical community.
The first book builds the basic geography and rules of the series: Hogwarts, Diagon Alley, wizarding families, houses, Quidditch and the uneasy boundary between magical and non-magical life. Harry's friendship with Ron Weasley and Hermione Granger becomes the emotional centre of the story as the three investigate a mystery hidden inside the school.
As an entry point to the world, this is the essential starting place. Almost every later book, film and game assumes familiarity with people, locations and events introduced here.