So, for most people this is a no brainer, but I'm a teacher and I know it can be a toughie for some. There is a HUGE difference between they're, there, and their. When I'm reading something and the wrong one is used, it irritates me to no end.
They're is a contraction. It actually means they are. They're going to school today.
There is a location. (It can fall under many different parts of speech.) The book is over there.
Their is possessive. Their books are in the car.
It's easy to write the wrong one when drafting, but it's important to know that spell check will not pick this up.
I hope this helps. Have a great day!!!!