Possessive nouns are used to show possession (owning, or having). They are words that would normally be nouns, but are used as adjectives to modify a noun or pronoun. Possessive nouns tell you who or what the modified noun or pronoun belongs to.
Example: The dog's collar is too large.
The word "dog's" is the possessive noun. It tells you that the noun "collar" belongs to the dog. The dog owns, or possesses the collar.
Add 's to the end of a singular noun to make it possessive.
Ex: The sky's color is changing...... sky + 's
Add 's to the end of a plural noun that does not end with an s.
Ex: We enjoyed the children's play...... children + 's
Add only the apostrophe (') to the end of a plural noun that ends with an s.
Ex: My sisters' names are Kate and Nikki...... sisters + '
Optional: If the noun is singular and ends with an s, add 's or add only the apostrophe (').
Ex: The bus's engine stopped. The bus' engine stopped. Note: Most sources recommend the shorter version if the ending "iz" sound is not wanted.