One click of the keyboard creates a hyphen. A hyphen looks like this: -. A dash is made with two clicks of the key and looks like this: —. This double hyphen is called an em dash because it is as wide as a capital M. A hyphen and a dash are not the same mark of punctuation. A hyphen is used to join parts of words, and a dash is used to join parts of sentences.

If you don't like the appearance of the two-hyphen pairing, Microsoft Word supports a real em dash. Go under Insert, then click Symbols to find it. But if you don't feel like searching the symbols, the — is perfectly acceptable.