An autobiographical novel is a special kind of book that is based on a real person's life but not everything in the book is exactly true. It's like when you play pretend with your friends and you make up a story but some parts of it are based on things that really happened to you. The author of an autobiographical novel writes about their own life experiences but they also add some made up parts to make the story more interesting.
For example, if the author wrote about a time they went on a vacation with their family, they might tell you about the fun things they did and the people they met. But they might also change some things, like adding a talking animal or making their family do something funny that they didn't actually do in real life.
Autobiographical novels are a fun way to learn about someone's life because they give us a glimpse into what it might be like to live in someone else's shoes.