Automatically format dashes while you type
To ensure that MS Word will automatically format dashes, open the AutoCorrect dialog box by holding down the Alt key and pressing T, then press A. Click on the AutoFormat As You Type tab and ensure that Hyphens with dash is selected, then click OK.
Type two short dashes and continue typing. When you press the space bar after typing the word following the two dashes, MS Word will change these dashes to a long dash.
Using Keyboard Shortcuts
To insert an en dash, hold down the Ctrl key and then press the minus (-) key on the number pad.
To insert an em dash, hold down the Alt + Ctrl key and then press the minus (-) key on the number pad.