Difference between "yours" and "your"?

• Your is a possessive adjective:

  Your car is black!

• Yours is a possessive pronoun:

  That car of yours is black!

It is "used to refer to a thing or things belonging to or associated with the person or people that the speaker is addressing".

Basically, those two sentences have the same meaning.

Yours is not a noun. It is a possessive pronoun.

yours |yôrz; yoŏrz| possessive pronoun 1 used to refer to a thing or things belonging to or associated with the person or people that the speaker is addressing : the choice is yours | it's no business of yours.

Your, on the other hand, is a possessive adjective.

A native English speaker would never say "the car of yours is black." The "car of yours" construction seems mainly to be used when the simpler construction "your car" is not available. For instance, "that car of yours": we can't say "that your car" or "your that car", so we have to say "that car of yours". But we can say "your red car", so we wouldn't say "the red car of yours".

I hope I have made myself clear! But the rules are complex. Compare friends, enemies, and brothers:

He's a friend of mine

and

He's my friend

mean the same thing: "he's one of my friends".

He's an enemy of mine

means "he's one of my enemies", but

He's my enemy

is not quite the same; it implies that he's my only enemy. This implication is not present in "He's my friend".

And lastly,

He's a brother of mine

is not something that you would ever say, however many brothers you had. (Perhaps it is possible if you have dozens of brothers, like the child of a Byzantine potentate. Otherwise it sounds very wrong to me.)