You often see words the words "They're", "Their", "There", misused or mixed up.
Here's a quick run-through to clarify the different usage.
They're is a conjunction of "They" and "Are". Joined they make "They're". When you meet this word, think: "they are".
Their essentially means "their own". Possessive form of they. When you meet this word, think: "their own".
There essentially means "over there". There indicates location. When you meet this word, think "its over there".
Putting it all together, this should clarify or totally confuse:
They're over there in their car.
They're means they are.
There means over there, the place I'm pointing to.
Their means their own, or their possession.
They are (the lot of them) over there (in that place) in their own car.
Its not so hard, once you get it.