My question is very simple. I just would like to know what do they mean by: "I believe you're up"
I've heard this expression in a movie and here is the script:
Well, he at least likes me, right? We're busy tomorrow night. Okay, and we're back. Amy, I believe you're up.
Oh, oh. Okay, I got this.
It's an idiom meaning "I've done my part, now it is your turn," or simply "It's your turn now, go ahead, do what you're supposed to do."
When during a soccer game the coach decides to let one of the players out on the field rest and motions him to get off, he will tap the substitute on the shoulder. The substitute will look up quizzically. The coach will say, "Okay, you're up." Now the substitute knows he needs to go out there and take the place of the player who needs a rest.
When during a joint concert one of the performers is almost finished with his number and is about to come off, the stage manager signals the performer whose number is next on the schedule and tell him, "Okay, you're up."
You're up means it's your turn http://www.urbandictionary.com/define.php?term=you+are+up
From the script you quote it sounds like the two people are commentators of some kind on the TV or radio. In an idle moment when they are not 'on air' they are discussing and then, abruptly they have to cut short their chat 'Okay, and we're back'. One of them then says to the other Amy, I believe you're up (i.e. Amy it's your turn to (...do whatever they do when they're 'on air')).
