At Kate Hofman's request, today I'm going to try to give a good, not-too-technical explanation of the uses of there, their and they're.
There=DIRECTION, PLACE OR FUNCTION:
Ex: Turn there to go to the mall. (direction)
I put it there. (place)
There shall come a time... (function to introduce a clause)
Ex.: It's their money. (they possess the money)
"To contract" means to shorten. "They're" is the shortened version of "they are."
Whenever you see the apostrophe in a word such as "they're," it is a contraction.
If you are uncertain whether this word is correct in your sentence, READ IT ALOUD,
using the words "they are." Your ear will tell you immediately if it is right.
Ex: Turn they are to go to the mall. WRONG
It's they are money. WRONG
They are going to turn there to go to the mall to spend their money. RIGHT
Now, contract "they are" to "they're."
They're going to turn there to go to the mall to spend their money. RIGHT