The dash is a rather emphatic piece of punctuation that can be used to draw attention to words and phrases in a sentence. Though admittedly it has more panache, the dash does little that a colon or a comma or two wouldn't do just as well. When you use a dash, you give your writing a somewhat informal tone. You should not use it extensively in formal or academic writing.

A single dash is effectively used to set off an illustrative or explanatory phrase at the end of a sentence—as a kind of punch line to the writer's point. A colon can be used this way as well.

The dash and gallantry of the cavalry charge, however out of place on a battlefield where rifled musketry and breech—loading artillery were fast becoming the rule, remained to plague armies well into the Second World War—a triumph of dogged conservatism over common sense.

If you begin a sentence with a string of adjectives or present participles, a single dash is the only appropriate piece of punctuation that will suitably connect these elements to the main part of the sentence.

State, corporate, cultural, scholastic, religious, military—all groups evolve or otherwise acquire a fundamental behavioural standard, adherence to which is the sine qua non of group membership.

Two dashes function similarly to inserting commas, setting off a phrase in the middle of a sentence that helps to define or illustrate the point you are making. Use double dashes for a quick aside or a sudden interruption into the thought of your sentence.

A world without armies—disciplined, obedient, and law-abiding—would be uninhabitable, and without their existence humanity would have to reconcile itself either to life at a primitive level or to a lawless chaos.

The dash can be created with either two hyphens (--) or the "Em Dash" (—) symbol in your word-processing program. Some programs, such as Microsoft Word and Corel WordPerfect, will automatically produce a dash when two hyphens are typed in sequence with no spaces on either side. There should be no space before or after a dash.