You're: contraction of you are.
You're certain that's right?
Your:
1. (a form of the possessive case of you used as an attributive adjective)
Your jacket is in that closet. I like your idea. Compare yours.
2. one's (used to indicate that one belonging to oneself or to any person)
The consulate is your best source of information. As you go down the hill, the library is on your left.
3. (used informally to indicate all members of a group, occupation, etc., or things of a particular type)
Take your factory worker, for instance. Your power brakes don't need that much servicing.
Be aware that you're and your are two different words
