Example 1
Harry's car was towed because he parked in front of a fire hydrant.
Since Harry is a singular noun, we add –'s to the end to show that the car belongs to Harry.
Example 2
Somebody stole all of the ballerinas' tutus.
With plural nouns that end in –s, simply add an apostrophe to the end of the word.
Example 3
In the '80s, Sheila couldn't leave her house without applying an entire can of hairspray to her bodacious side ponytail.
In this retro example, we use an apostrophe to show that we've shortened 1980s to '80s by omitting the 19. The contraction couldn't also uses an apostrophe to show that we removed the o in not before making the contraction.