Narrative is also called action. It's what a character does, moves, etc.
An example would be:
Judd moves to the door, waiting, dreading the moment when Casey will walk in.
A slugline is the scene heading in a script. Either term is acceptable.
An example of a slugline is:
INT. CLASSROOM - NIGHT
A transition is a line or word that describes movement between scenes.
For example:
DISSOLVE TO:, CUT TO:, HARD CUT TO:
Transitions are placed on the far right margin on a line by themselves. These days, transitions are used much.
V.O. means VOICE OVER. It is used to modify the speaker.
For example:
MANNY (V.O.)
I knew I was in trouble as soon as I met him. He was bad - you could smell it on him.
A voice over narrator is not seen although it could be one of characters in the film. The narrator of "STAND BY ME" is an example of a person who isn't directly seen in the movie although his younger self is.