Examples of contractions:
- She hasn't (=has not) visited her parents for a few months.
- Mike didn't (=did not) remind me of the appointment.
Examples of possessive case of a noun:
- My brother's birthday is drawing nearer and nearer.
- The child's toys collectincluded a teddy bear and a plastic dinosaur.
In order to form the possessive case of a plural noun ending with an "s", simply add an apostrophe after the "s".
- One of the drivers' main problems are the high gas prices.
- My grandparents' house was sold shortly after she died.
It is a very common mistake among ESL students (and sometimes native speakers as well) to use an apostrophe to create possessive pronouns. For example:
- The dog was on the lawn, wagging it's tail.
"it's" is the contraction of "it is". That's why:
- The dog was on the lawn, waging its tail.
Now, this is correct.
Similarly, the other possesive pronouns are "hers", "yours", and "theirs".