Dave Wilton links to a fine rant in The Atlantic about hyphens. (Yes, we care.) And that link will get you to this one in Mental Floss about the difference between the em-dash and the en-dash.
Now I am careful to use the en-dash when separating ranges of numbers, such as an article being on pages 317–24 of a journal (although you can’t see the difference in this font), but how did I get through various writing and editing jobs without knowing about “the storied ‘compound adjective hyphen,’ an event so rare in the English language that proofreaders shiver with excitement whenever they come across it”?
Me with a copy of The Chicago Manual of Style always within reach. I am but an egg.