Grammar Blog

Their and There and They're. Similar to my problem with its and it's. Very similar words, very different meanings.
Their-possesive. That is their lawn chair.
They're-conjunction- They're (They are) over there.
There-There goes the ball.

You don't want to mix them up, because you it looks pretty bad. I used to mix them up and my teachers would always want to know why "they are lawn chair" and how they become a lawn chair. Very embarrassing. So keep 'em straight.

Washington State University
http://www.wsu.edu/~brians/errors/their.html