Use: We use possessive pronouns/adjectives and the possessive form of a noun to show that something belongs to someone or something.

's is added to the end of singular nouns and irregular plural nouns:
castle ► castle's moat
boss ► boss's desk
men ► men's locker room

' is added to regular plural nouns:
cars ► cars' windshields
bees ► bees' wings

Note: Only add an s to the pronoun it.
Its contents are under the scrutiny of authorities.

It's not what you think. = It is not what you think.

Possessive pronouns/adjectives:
I have a large house. >> My large house costs too much to heat in the winter.
You are guilty. >> Your guilt is obvious.