Possessives are a grammatical form that indicate ownership or belonging:
my parents’ house
my mother’s mother
Use an apostrophe plus s to form the possessive of a singular noun or a plural noun that does not end in s:
Hillel’s questions
children’s memories
Many writers prefer to add an apostrophe plus s to form the possessive of a singular noun ending in s, although the final s is not strictly required. Ask your instructor how to handle these words or, if you are writing for a particular publication, such as a newspaper or journal, look at how the publication handles possessives:
the class’s assignment
Use only an apostrophe to form the possessive of a plural noun that ends in s:
bloggers’ points of view
Americans’ attitudes