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Stop! Now re-read the title of this post—at least 3–5 times—then let it sink in before continuing.

You should note that the sentence above illustrates the proper use of the hyphen and the two main types of dashes—the en dash and the em dash. They must not be confused with each other, nor should they be confused with the hyphen (-), which is used to join compound words together.

An en dash, named for the width of a typesetter’s n key, is a little longer than a hyphen. It is used for periods of time when you might otherwise use to.

Examples:
The years 2001–2003
January–June

An en dash is also used in place of a hyphen when combining open compounds.

Examples:
North Carolina–Virginia border
a high school–college conference

An em dash is longer than an en dash (named for the width of a typesetter’s m key). In general, use of the em dash should be sparing so that it does not lose it’s power of emphasis. Em dashes may replace commas, semicolons, colons, and parentheses to indicate added emphasis, an interruption, or an abrupt change of thought.

Examples:
You are the friend—the only friend—who offered to help me.
Never have I met such a lovely person—before you.

There are no spaces before or after en or em dashes although, a designer may insert thin space or slightly kern around the dashes to improve readability.