There are a couple of idiomatic meanings for this expression. One is "you're awake." So you can ask if Mary is already up, and someone might reply, "No, she's still asleep." ... or sometimes, when you walk into a room, people say, "Oh, you're up. We thought you were still asleep."
The other meaning of you're up is it's your turn to do something. For example, if you're playing a board game, and it’s you’re turn to roll the dice, you’re friends may say, “Ok, you’re up.” This means you’re next to pick up the dice, roll it and play.
A: Hi Tom. I didn’t think you’d be up this early to watch the game.
B: I know. I worked until midnight last night, but I wanted to watch my son play baseball.
A: He’s the kid with the Yankees cap on, right?
B: Yeah, that’s Johnny. I try to make it to all his games.
A: How’s work?
B: Work’s alright. We’ve been really busy lately.
A: Oh, Johnny’s up next. Let’s watch this.
B: Alright. Let’s go, Johnny!
board game - a game like Monopoly or Scrabble that's usually played on a table
dice – white cubes with black dots on each side
Alright folks, the next time someone asks if you’re asleep, say “No, I’m up.” … and when you’re playing a game, you can ask, “Who’s up next?”Enjoy the weekend.