you're and your

You're is short for you are.
Your shows that something belongs to "you" or is related to "you" (e.g., your car, your father).

You're and Your

Some writers are confused by you're and your. A mistake involving these constitutes a grammatical howler.

You're

You're is a contraction of you are. It has no other uses. This is a 100% rule. If you cannot expand it to you are in your sentence, then it is wrong.

Examples:

Your

The word your sits before another word (usually a noun or a pronoun) to show that it belongs to "you" (e.g., your car, your arm), is of "you" (e.g., your picture, your photograph) or is related to "you" (e.g., your uncle).

Your is a possessive adjective. (Other possessive adjectives are my, your, his, her, its, our, and their.)

Examples: