Imagine the following situation:
A friend asks you if he/she can borrow your bike for a day. You don’t mind it. How would you let your friend know it’s OK for him/her to take your bike?
Here’s a few options:
Sure, no problem at all.
Yeah, go ahead.
It’s all yours.
Take your pick!
P.S. Naturally, you can use these expressions in any other situation similar to the example given here.