Your and You're both have the same sound when spoken. Their meanings are completely different.
You're going to be twenty years-old this year.
Your dog is very hungry.
You're = You are. This comes from the verb "To Be".
You're very cold.
You're going to run today.
* You can use You're with adjectives.
You're + adjective( Description )
You're beautiful.
You're happy.
You can use You're with actions.
You're + Verb -ing( continuous action )
You're cooking food.
You're fixing the car.
Your is a possessive pronoun. It shows ownership of something.
Your car is blue.
Your cat is very funny.
Possessive pronoun = car
Possessive pronoun = cat
* The possessive pronouns always comes after your.