Here is a simple post that will help you determine when to use there, their, or they’re.
We are going over there. (“There” being a place, location, etc.)
I used their paper because I did not have any of my own. (“Their” being someone else that the item in question belonged to.)
They’re going with us. Would you like to join? (“They’re” being short for “they are.”)
As promised, super simple.