Dashes are not to be confused with hyphens. Dashes have other uses altogether.
The en dash (N-dash) is a short horizontal line that is the width of the letter N.
It is commonly used to indicate a range of numbers, including times and dates.
Note that there are no spaces on either side of the en dash for such use.
In Microsoft Word, go to Insert Symbol and scroll way down until you get to the en dash, or type in Unicode (hex) #2013.
Work hours are Mon.–Fri., 8:00 a.m.–5:00 p.m., with one hour off for lunch.
Do not use an en dash if you express the range using the words “from X to Y” or “between X and Z.”
The em dash (M-dash) is twice as wide—the width of the letter M. No spaces are used on either side of it, as it’s plenty wide enough by itself.
Em dashes are used to set off a parenthetical expression in the middle of a sentence. In Word, the em dash is Unicode (hex) #2014 when you do Insert Symbol.
The compressors will arrive in Qatar August 11—the first day of Ramadan—late in the afternoon.
Em dashes are also used to camouflage identity, mark where somebody is interrupted by someone else, or show that someone stops speaking in mid-sentence.
S— informed police that the gang members were planning a rumble Friday night.
“Janie said she might not get here until—” Ding-dong! “Oh, that must be she now.”
And then there’s Darth Vader’s line in the movie Star Wars Episode IV: A New Hope:
“I sense something, a presence I have not felt since—” and then he turns and walks away with a sweep of his black cape.
Sometimes en dashes are used mark off an “aside,” or parenthetical expression – such as this one – instead of an em dash, especially in narrow columns.
In such situations, en dashes have a single space on either side.