apostrophe

I always forget when writing where to put the apostrophe, is it before or after the "S" that makes it possessive.

For example:

Apostrophes are used to make nouns possessive, to show ownership. When nouns are singular, we generally add an apostrophe and the letter "S" to indicate possession:
* Jeremy's laundry took forever to dry.

When singular or plural nouns end with the letter "S," we most often drop the final "S" after the apostrophe

* The horses' hooves were shiny. (More than one horse has hooves.)

Here is a web site that has examples on where and when to add a apostrophe.