This book is a superb all-in-one guide to success GCSE English Language and English Literature - GCSE English 2003

Apostrophes
Section Ten — Language and Grammar

Lots of people get apostrophes wrong. You need to get them figured out to get more than a C.

You’ve Got to Add’s to Show Who Owns Something

It Gets a Bit Tricky with Groups of People or Things

Apostrophes Can Show Where There’s a Missing Letter

1) You can shorten some pairs of words by cutting out letters.

2) You put an apostrophe to show where you've removed the letters from.

WARNING — Don’t Use Apostrophes for Anything Else

Make sure you know how to use apostrophes properly

You must use apostrophes, and you need to use them correctly. Just think how some songs would sound without them — "Cannot get you out of my head", "Do not stop moving, everybody is grooving", etc...