When should you use they're? They're is a contraction of they are so you can only use they're is when you to say they are. e.g They're really funny I loved that last joke.
When should you use their? Their is used to show possession it is just like using my your or his. If you want to find out when to use their replace it with our. You will be correct because our is used to show possession.When should you use there? The word there represents a place. e.g There are two apples.