The possessive case shows ownership or a relationship between things. It is typically formed by adding an apostrophe ('s) or just an apostrophe (') to a noun.
Examples:
John's book (The book belongs to John).
The teachers' room (The room belongs to the teachers).
Usage:
Singular nouns: Add 's - (The cat's tail.)
Plural nouns ending in "s": Add only an apostrophe (') - (The students' classroom.)
Irregular plural nouns: Add 's - (The children's toys.)
