We've been seeing some manuscripts with improper apostrophe usage lately. Here are the rules for apostrophes and possessives.
Apostrophes are used in contractions, that is a shortened version of two words, but never in abbreviations. Can’t instead of can not, it’s for it is (the possessive form of “it” never takes an apostrophe), and didn’t instead of did not. But CDs wouldn’t take an apostrophe.
Apostrophes (usually apostrophe followed by an s) are used, for possessive clauses. Mandy’s house. Tammy’s CDs. Do you see what I mean?
Possessive forms of proper names take an apostrophe s even if they already end in s, such as Silas’s car. But plural nouns and pronouns get the apostrophe without the s in the plural form. I visited Mandy’s parents’ house.
Plural form of proper names get an “es” rather than a plain s, and no apostrophe.
Both the following are correct. “The Williams’ car,” for possessive, and “The Williamses came to dinner,” for plural. I know, confusing isn’t it?