Apostrophes in English have many rules, along with exceptions to these rules. Anyway, their two main uses are:
1] To show that some letters have been taken out of a word to shorten it.
The apostrophe goes where the letters have been removed, e. g.
- is not becomes isn‘t
- do not > don’t
- I would like to > I‘d like to
2] To show belonging.
To do this, we usually add ’s.
- the horse’s tail – shows that the tail belongs to the horse
- Paul‘s bike is …
- Jen‘s brother works as …
In words that end in -s apostrophe goes after the -s that is already there, e. g.:
- The octopus’ legs are thin = the legs belong to the octopus