Let's consider the following example:
Ex: The child's book / Juan's bookAS seen , in english, first we put the possessor followed by the apostrophe ' and 's', when the possessor is in singular. When the possessor is plural, just the apostrophe. After this the thing possessed.
Ex: The student's new pencil / Mary's brother
My parents' house.
(Refers to the house that my parents have.)
REMEMBER: The apostrophe + s is added to singular nouns and just the apostrophe to plural nouns
This structure is used with people and animals, though it can also be used with places, organizations and companies.
Otherwise, if the possessor is not a person, the Saxon Genitive is not used.
Ex: The legs of the table -NOT-The table's legs
To sump up, let's take a look at this Summary Grammar chart