Use possessive adjectives with nouns:

My car is old.

Its color is white.

Her eyes are green.

That's my book.

Are these your keys?

This isn't our money.

Are those their things?

Because pronouns are substitutes for nouns
and are used in place of them, use possessive pronouns alone:

Bill's car is new. Mine is old.

His eyes are brown. Hers are green.

That isn't Fred's book. It's hers.

These aren't my keys. Are they yours?

This isn't Bob's money. It's ours.

Those aren't my things. Are they theirs?

Possessive nouns with 's, s', or ' can also be
used like possessive pronouns:

Bill's car is new. Dennis' is old.

His eyes are brown. Jane's are green.

That isn't Fred's book. It's Bess'.

These aren't my keys. Are they Tom's?

This isn't Bob's money. It's his parents'.

Those aren't my things. Are they Joe's
and Jim's?