The author tells the story of a series of events, usually presented in chronological order. In a novel however, chronological order may be violated for the sake of the plot. The emphasis in narration, in both fiction and non-fiction, is on the events. Narration tells what has happened. Its primary purpose is to tell a story.
Exposition presents the facts about a subject or an issue as clearly and impartially as possible.
Its primary purpose is to explain. The author uses the techniques of persuasion to establish the truth of a statement or to convince the reader of its falsity. The purpose is to persuade the reader to believe something and perhaps to act on that belief. Argument takes sides on an issue. Its primary purpose is to convince.