How do you get from "Who's under R2D2?" to voice dubbing in iMovie?

Isaac: Who's under R2D2?
Me: Under?!
I: Yes, who's the real one under R2D2?
Me: Oh, you mean who's the person controlling him?
I: Yes
Me: I don't know
I: Well, who's under Obe Wan Kenobi?
Me: Ah, I know that one. That's a man called "Alec Guiness"
I: And who's under Luke Skywalker?
Me: Ah, I know that too. That's a man called Mark Hamill
I: And who's under Darth Vader
Me: Hmm…that's complicated. The man dressed as Darth Vader is a very tall man from Somerset, but I don't know his name. But someone different does his voice.
I: *thinks* What do you mean? Does he hold something? (I assume he means a microphone or speaker or something).
Me: No. They….hmm….let me show you…

This…THIS is why nothing ever gets done in our house!