When you tell friends that something is up to them, you're telling them to make the decision. You say this expression to let other people decide what to do either because the decision doesn't matter much to you or you just don't want to be the one to decide. For example, if you're about to watch a movie with friends and you don't mind watching any of the available choices, you can say, "It's up to you guys. I really don't mind watching any of these." One of your friends can then decide which movie to watch and hopefully, everyone will be happy with it.
A: What time do you want to meet up this weekend?
B: It's up to you. My schedule's flexible this weekend.
A: What about at noon? ... so I can sleep in.
B: That sounds good. I can run some errands in the morning if I wake up early.
A: Alright. Let's meet at noon, then we can check out the farmer's market on Union Square before we head over to Tim's place.
B: Sounds good. Should I bring some beer or something?
A: It's up to you. We can always run to the store if we need anything.
B: Ok. See you Saturday then.
meet up - meet to spend time together
sleep in - wake up late
run errands - do a list of things outside the house such as go to the post office, the bank, etc.
check out - see; examine
head over - go to
Alright, everyone. As far practicing, it's really up to you. But I think you should.
Enjoy your weekend.