Narration is basically like rping with someone else. But the NPC acts as a a narrator to the story, they will guide you through what has to be done. They may control you to get you to a place where the story needs to go, but otherwise, you are in control.
Basics
The NPC narrator will set the scene for you. They may also give you some people to talk to, who they are in charge of. They will lead the story to where it needs to go, if it somehow gets off track, but usually, if there are other people in the thread, they will rp as little as possible, if only to get some storylines points in.
If you have any questions, please let me know in here.