The Apostrophe

The apostrophe (that’s this little sign here: ‘) is normally only used to show possession or omission.

Example sentences:
This is my colleague’s office. (possession)
We watched the boys’ football team. (possession)
There’s a lovely lamp on her desk. (omission)
They grew up in the ’90s. (omission)

We don’t normally use apostrophes to form plurals.

Example sentences:
We bought eggs, mushrooms and peas in the supermarket.
This book was written in the 1990s.

However, apostrophes can be used to avoid confusion or misreading:

She received two A’s, three B’s and two C’s.

I hope that helps!