If you mean if you've just taken the opponent's Queen with your peice, Then it means you win. Thats how you win, Capture the queen.
What happens if you are a queen up

Well lots of ppl resign, but its hard to say, don't give ip, u may win on time.... , if u have more pieces on the board then ur enemy then u have a chance of a draw,

What really happens when you are a queen up--and presuming your opponent hasn't sacrificed his queen for a mating attack--you simply start exchanging pieces of equal value until he's busted.

yep, chop wood as I call it, or just defend, or attack, How many of you here have a USCF Rating, if so please put it down,

You have like a 80-85% chance of winning if you still have most of your minor peices, im jsut guessing haha but it all just depends.
In the recently completed US team championship semi finals match there was a queen sacrifice.
Opponent resigned shortly afterwards.
So a queen up may not be wonderful every single time.

I have to share this.
Of course, if you get 2 pieces and 3 pawns for her, it's not as bad. Still, a nice game.
What do you do when you are a queen up?