The punctuation mark used to show possession or form contractions such as “don’t” is an apostrophe.
In contractions, the apostrophe marks letters omitted from a shortened expression. Don’t comes from do not, can’t from cannot, and I’m from I am. The mark helps readers recognize that the written form represents two words that have been joined and shortened.
Apostrophes also mark possessive forms in English. In the cat’s bowl, the apostrophe signals a relationship involving the cat; in the teachers’ lounge, it follows the s because teachers is already plural. This use is traditionally called the possessive, although it often expresses relationships other than literal ownership, as in today’s news or the school’s headmaster.
A frequent mistake is writing it’s when the intended meaning is possessive. It’s means it is or it has, while its is the possessive pronoun: “The dog wagged its tail.” Possessive pronouns including his, hers, ours, theirs, and whose do not use apostrophes. Hyphens join words, colons introduce explanations or lists, and commas separate elements.