Rules for Using Apostrophe
The apostrophe has 2 functions:
One is to show possession/ownership and the other is to show omission of letters or words.
1. An apostrophe shows ownership:
Ayon’s new shoes are red.
1a. These are the student’s books.
Several books belonging to 1 student.
1b. These are the students’ books.
Books belonging to a group of students.
My 3 friends’ shirts are blue.
More than 1 friend.
The lions’ Den (More than 1 lion)
Amos’ books (instead of Amos’s books)
Sometimes a name ending on an s is given an apostrophe instead of an additional s and apostrophe as seen in the name Amos, typically both are correct.
1c. Add an apostrophe to the end of plural nouns that end in s:
Boys’ hats. Players’ uniforms
2. An apostrophe is used in contractions when a word or letter(s) is missing:
2a. Don’t go outside. (Do not)
I’ll finish my homework later. (I will – I’ll)