Fiction is the genre in which the stories are not true. Nonfiction is concerned with real events and stories.
Some other genres are mythology and fantasy. Mythology is all about myths; myths are stories that some people make to account for different things in the world. Many myths are related to some supernatural beings. Fantasy is a genre of which writers write about a fiction character on an utterly unknown planet, or contain things that are untrue, such as dragons and dwarves.
Examples of fantasy books are Harry Potter and The Lord of the Rings. Contrarily, The Adventures of Christopher Columbus is a nonfiction book. Many books written by Horatio Alger are fiction,
Most books I have read this year are fiction, for all of those books happened in a real setting, only the characters and events were not real.
Genres are useful to find one's favourite books.