Sometimes, it’s the tiniest details of grammar that give you the biggest headaches. Apostrophes are so little, but they can be a surprisingly enormous pain. Learn the rules for using apostrophes when it comes to indicating possessive nouns, contractions, verbs and plural nouns, and you will have mastered a very important part of grammar.
When it comes to contractions, think of apostrophes as signifying the missing letter. More specifically, think of apostrophes as signifying the missing vowel. People often use contractions in speech, as well as in more informal, casual style writing. So instead of writing “did not,” you may write “didn’t.” Notice that the two words were pushed together, and the apostrophe now occupies the place of the second word’s vowel. So “should not” becomes “shouldn’t,” “he is” becomes “he’s,” and “they are” becomes “they’re.” And put an apostrophe on the end of “it” when you’re forming a contraction, so that “it is” becomes “it’s."
Always use an apostrophe when you’re trying to indicate that something belongs to someone or something else. For example, if a mansion belongs to Susie, you would call that mansion “Susie’s mansion.” If a mansion belongs to both Susie and John, it's called “Susie and John’s mansion.” If Susie and John own separate mansions, those mansions would be “Susie’s and John’s mansions.” If a yacht club owned a mansion, you’d call that mansion “the yacht club’s mansion.” There is one very important exception: If you use possessive pronouns, then you don't use an apostrophe. For example, if a yacht club owned a mansion, you would call the mansion “its mansion” -- not “it’s mansion" -- and Susie's mansion is "hers," not "her's."
Unless you’re using a verb as part of a contraction, the only time you would use an apostrophe with a verb is if you were trying to shorten it -- in other words, if you were using slang. (Or, to put it more casually, if you were usin’ slang.) Here, you drop the “g” at the end of “ing” and replace it with an apostrophe. There are very, very few instances where you would want to do this. Perhaps as part of the colloquial dialogue in a piece of creative work, you might write “He’s runnin’ away” instead of “He’s running away,” or “They’re goin’ off the deep end” instead of “They’re going off the deep end.” But this type of slang should be used exceedingly sparingly and only in specific instances to serve a clear rhetorical purpose since it isn’t grammatically correct and is generally not accepted in formal writing.
Now that you’re getting the hang of apostrophes, you may want to put them on the end of every word that ends in “s." Well, fight that urge. Apostrophes aren’t meant to signify multiple people, places, or things -- that is, they’re not meant to signal plurality. Never use an apostrophe to indicate that there is more than one. For instance, the sentence “A hundred dancers and thirty orchestra members took part in six ballet performances of 'The Nutcracker' in two cities” is correct; the sentence “A hundred dancer’s and thirty orchestra member’s took part in six ballet performance’s of 'The Nutcracker' in two cities” is incorrect.