When you tell a story or describe something out loud, you narrate. You might hire a well-known actor to narrate your documentary film about circus elephants.
One way to narrate is to comment on or describe visual images — photographs or scenes in a film, for example. You can also narrate a story simply by relaying the details aloud. In books, a character sometimes narrates the story as well. It appears that narration, or the action of telling a story, came before narrate, from the Latin root narrare, "to tell, relate, or recount," or literally, "to make acquainted with."