His and her are possessive pronouns and we use them when we want to show that somebody possesses something. His is used when a boy or man possesses something.
Example: John has a car. It is his car.
Her is used when a girl or woman possesses something.
Example: Mary has a car. It is her car.
You can read more about possessive adjectives and do a quiz here.
His can also be a possessive pronoun. Again it shows that a boy or man possesses something. However, we do not put it before the possessed object.
Example: It is his car. (possessive adjective)
This car is his. (possessive pronoun)