When to use an s' or 's?
s' is used as an apostrophe for a word that refers to plural
form, for example saying The girls' toys. In this instance it
refers to the toys of more than one girl. You would also use s' for
names ending with an s, such as Tess' toys.
's is used as an apostrophe for a word that refers to singular
form, for example saying The girl's toys. This refers to the toys
of just one girl. You would also use 's with names such as Tom's
toys