When something belongs to someone we use: 's or '
1. When it belongs to a person or an animal (enkelvoud en meervoud)- Girl's watch - Dog's tail
- children's toys
2. When the word ends on s in plural we only use ' (no s!)
- Girls' watch
- Dogs' tail
3. For things and names of places we use: OF
- The Prisoner of Azkaban
- The key of this door