Apostrophes are used with singular and plural nouns to show ownership or possession; for example,

working memory's limitations = the limitations of working memory
Winchester's argument = the argument of Winchester
the policies' details = the details of the policies.

Some of the most common errors in punctuation relate to using apostrophes to signal ownership or possession.

Apostrophes are also used in contractions, such as it's (it is), I'm (I am), can't (cannot). While the use of contractions is not encouraged in academic writing, the difference between the contraction it's and the possessive pronoun its is often confused.