Someone asked me recently about one particular hyphen use—the suspended hyphen. Here’s an example of the suspended (a.k.a. “hanging” or “floating”) hyphen in use: “First- or second-year students may apply for parking spaces after October 1.” The suspended hyphen is employed for compound adjectives* preceding a noun when the compounds share the same second word, conveniently saving you from tedious repetition (“first-year or second-year”).
*The presence or absence of a hyphen can change the meaning of a phrase (or sometimes help avoid ambiguity): a “useful punctuation post” without the hyphen means a useful post about punctuation, whereas a “useful-punctuation post” means a post about useful punctuation. Grammar Monkeys has a regular “why we need hyphens” feature (“because an anti-child-abuse program is not the same as an anti-child abuse program”).