Your is an adjective. Your is the possessive form of the pronoun you.
Your may be used as a modifier before a noun: "Put on Your jacket." "You may list Your accomplishments."
Your may be used to indicate something that belongs to a person/one/thing. "Your best chance here is to punt." "The best view is on Your right." "All right, Rover, this is Your doghouse."
Informal: Your may be used to indicate a type or situation familiar to the addressed. "This is Your basic rowboat here." "We are in Your typical mess here." [Note: The use of Your, here does not really indicate that which belongs to you. In this case, Your is used to indicate possession of general knowledge, rather than specific possession.]
Correct: "Your car is the fastest of the three." [The car that belongs to you is the fastest of the three.]
Incorrect: "You car is the fastest of the three." [You is not the possessive form. Your is the possessive form.]
Incorrect: "You're problem is that you always assume that there will be no problems." [You are problem is that you always assume that there will be no problems. No!]
Correct: "This is Your chance!" [This is the chance that belongs to you.]
Incorrect: "That is you're problem." [That is you are problem. No!]
Yours is a pronoun. Yours may be used with either a singular or plural verb.
Yours is used to indicate the one or ones belonging to you (singular). "Yours are the blue ones." "The choice is Yours."