Their = belonging to them.
There = a location, such as “over there”.
They’re = a contraction of they + are.
Example: They’re going there to get their stuff.
While we are at it….
Two = a number, also known as 2
Too = also
To = all other uses
Example: She needs to go number two, too.
(Ok, that was a bad example….if you can do better, let me know)