Typographers use different dashes for different purposes. The only difference between the dashes is their width. For instance, you get one type of dash when you press on the minus key-it is a dash that is very narrow. A longer dash is called an en dash, because it is the same width as a lowercase n. An en-dash is typically used to denote ranges of numbers. Wider still is the em-dash, which is just as wide as a lowercase m. The em-dash is typically used in sentences, as a dash between clauses.
To insert an en-dash in your document, hold down the Alt key and type 0150 on the numeric keypad; an em-dash is produced by holding down the Alt key and typing 0151. You could also use the Special Characters tab of the Symbol dialog box to add the dashes.
You may be familiar with using em- and en-dashes from working with Word. They work the same way in Excel. The only caveat is that when you use special dashes (as opposed to a regular minus sign), Excel automatically treats the information in your cell as text.