Narration is the act of telling a story, usually in some kind of chronological order. Making up a scary ghost story and relating it around a camp fire is an act of narration.
Narration generally means any kind of explaining or telling of something. It is usually used in reference to storytelling. If you've ever watched a television show where one character's voice talks directly to the audience, then you've heard narration. You will often find narration happening in songs where the singer is telling the story of how something happened — like the day he lost his guitar, his truck, his wife, and started singing the blues.