Possessive pronouns can be used as subjects or as objects in a sentence:
Your class is in the evening. Mine is in the morning.
(Mine = My class; "Mine" is the subject)
She didn't have a pen, so I gave her mine.
("mine" is a direct object)
All the other prossessive pronouns end in an "s:" yours, his, hers, its, ours, yours, theirs.
Possessive pronouns are often used alongside possessive adjectives. It's important to know the difference. For example: His car is parked outside. Hers is in the garage. In the first sentence, "His" is a possessive adjective. It comes before a noun. In the second sentence, "Hers" is a possessive pronoun and you don't use if before another noun.
Look at this mistake:
Hers car is in the garage. You should say, "Her car is..." This is a very common mistake. The person speaking is confusing the possessive adjective with the possessive pronoun.