You're is the contraction for "you are."
Your shows possession, something belongs to you or is related to you (e.g., your car, your father).
You're is a contraction of you are. It has no other uses. This is an absolute rule. If you cannot expand it to you are in your sentence, then it is wrong.
The word your sits before another word (usually a noun or a pronoun) to show that it belongs to "you." Your is a possessive adjective. (Other possessive adjectives are: my, your, his, her, its, our and their.)