A diary is a daily journal of one's thoughts, feelings, moods, actions, activities, and so on. It is not usually intended for an audience. It's personal. Many people go out their way to keep it that way. An autobiography is a book about a person's life that can include information about themselves given to them from others like parents, bosses, friends, and relatives. It can also include thoughts, feelings, and moods and other subjective observations which are usually expressed within the context of events, actions, and activities. It's written by the person whose life it's about with the intention of being published. Hope this helps.
Well.. A diary is what you right in everyday like, a journal a Autobiography is a book about a person, celebrity, etc.