There’s a difference between hyphens and dashes. Most people insert a hyphen where they should use an em dash or an en dash.
An em dash looks like a hyphen but is longer – it’s as wide as the letter m.
An en dash is the width of the letter n. Use en dashes to show inclusive numbers or time periods, like so: pages 45-50; Aug.-Sept. 1998; Exodus 16:11-16:18. An en dash is a little bit longer than a hyphen.
To create an em dash press Alt+Ctrl+- (the minus sign key on the Numeric keypad) ,
to create an en dash press Ctrl+- (on the numeric keypad)
source Microsoft Office 2003 All-in-One Desk Reference For Dummies, by Peter Weverka.