The possessive case
The possessive case shows ownership. The rule is as follows:
If the noun doesn't end with S, add ‘S to the end of the noun.
Example: Moussa's book
The pupil's bag
If the noun ends with S, you can either add ‘S or just add an apostrophe to its end.
Example: Chris's friend
Chris' friend
Plural nouns ending with S just take an apostrophe.