Possessive pronouns never take an apostrophe. Remembering this will help you avoid some common confusions.
Its is the possessive pronoun of it. It's is a contraction of it is.
The dog is chasing its tail.
It's raining cats and dogs.
Whose is the possessive pronoun of who. Who's is a contraction of who is.
Whose house is that?
Who's in the house?
Your and yours are the possessive pronouns of you. You're is a contraction of you are.
Your pizza is ready.
You're eating a pizza.
The pizza is yours.
Their and theirs are the possessive pronouns of they. They're is a contraction of they are. There indicates location. There's is a contraction of there is.
Their mother will drive them to school.
That car is theirs.
They're driving to school with their mother.
There is their mother now.
There's their mother now.
