The Apostrophe is used to denote the possessive case of nouns.

Here is a lock of Arthur’s hair.

Have you read Prof. Nalin de Silva’s latest speech?

# It is used to show that a letter has been left out.

Don’t try, if you can’t do it.

You shouldn’t talk like that.

She’s done it and it’s not fair.

“{'s
1. Is: She's here.
2. Has: He's arrived.
3. Does: What's he want?
4. Us: Let's go.}”

# It is used to mark the plural of figures and letters.

You should mind your P’s and Q’s (Be careful what you say or do).

You don’t make a clear distinction between your p's and q's.

These 5’s are written in a different hand from the 3’s.