The dash may be used to set off parenthetical material that deserves special emphasis. When typing, use two hyphens to form a dash (--), with no space before or after the dash.
Use a dash to introduce a list, to signal a restatement or amplification, or to indicate a shift in tone or thought.
Peter decided to focus on his priorities—applying to graduate school and getting financial aid.
Kiere took a few steps back, came running full speed, kicked a mighty kick—and missed the ball.
In the first example, the writer could instead have used a colon. The colon is more formal than the dash and not quite as emphatic.
Use a pair of dashes to set off parenthetical material that deserves special emphasis or to set off an appositive that contains commas.
Everything in the classroom—from the pencils on the desks to the books on the shelves—was in perfect order.