Possessives tell us who owns something. They also tell us about relations between people.
The subject form is used in front of a noun.
The object form is used alone.
Subject form Object form
It is my family. This family is mine.
Are they your parents? Ok, they are yours.
Is it his dog? Yes, the spotted dog is his.
It is not her son? Yes, it is hers.
The dog loves its new ball.
Where is our son? The boy to the right is ours.
Is it your dog? I did not know he was yours.
Look, their dog is small! Are you sure that dog is theirs?