Quoting from this page: Grammar: Confused Words
Your is a possessive meaning "belonging to you."
You're is a contraction of "you are."
Is this your hairbrush?
You're not using my hairbrush, are you?
"Than" is a comparative term. Use it only when you're making a comparison between two or more things.
I am shorter than Xena.
There are more cherries in my bowl than in Gabby's.
"Then" is a temporal term. Use it to indicate that something happens after something else, often with a cause-and-effect relationship. Also use it in conditional statements (after "if" clauses).
Xena looked around and then mounted Argo.
Xena entered the room. Then everyone else left.
If you're traveling with Xena, then you must be pretty brave.