Possessive apostrophes indicate ownership. Typically, this will involve adding an apostrophe plus the letter ‘s’ after a noun or someone’s name:
Mandy's hair was tangled.
The table’s leg is wobbly.
Here, for example, the apostrophes show us that the hair belongs to Mandy and that the leg belongs to the table.
The main variation on the rule above comes when a word already ends in the letter ‘s’. In this case, you can either:
Add an apostrophe plus another ‘s’ (e.g. Denis’s tennis racquet)
Or just use the apostrophe by itself (e.g. Denis’ tennis racquet)
Both of these are accepted in modern English. However, if you’re writing an essay or for a specific publication, you may want to check your style guide for advice on which approach to use.
Plurals that end in ‘s’ sometimes cause confusion when using a possessive apostrophe. The key here is that possessive apostrophes should always go after the final ‘s’ in a plural. For instance, imagine if we wanted to talk about two dogs with empty food bowls:
The dogs’ bowls are empty. ✓
The dog’s bowls are empty. ✗
The first sentence here suggests multiple dogs and multiple bowls. But the second implies one dog with more than one bowl. And while this not ungrammatical, it is still an error as it does not say what it is meant to say.