Pronouns in English display case according to their function in the sentence.

Subjective Pronouns: They act as the subject of independent or dependent clauses.
example:

• I will meet you later.

In this example both I and you are pronouns but I is a subjective pronoun because it functions as a subject, the person or thing who realizes the action.
example:

• He travels to Spain once a month.

In this example he is a subjective pronoun because he is the person who realizes the action (he travels.)

Possessive Pronouns: They show possession of something else.
example:

• The art book that is on the table is hers.

Hers is a possessive pronoun because it indicates that the art book belongs to her.
 

• Please do not take those flowers because they are mine.

Objective Pronouns: They function as the recipient of the action.
 

• Kristen gave Eric and me a couple of tickets to see Pink Floyd in concert.

• The bandits released two hostages: her and her sister.

Pronouns change form when they change case. These changes are illustrated in the chart bellow: