—This is an em dash. It is the width of a capital M.
–This is an en dash. It is the width of a capital N.
-This is a hyphen. It is the width of… er… a hyphen.
The hyphen is not a dash. It’s a hyphen—used to hyphenate things; intra-word punctuation, generally. It is not a replacement for any of the dashes.
Back in the day, when I was at uni, I handed in an assignment. It came back with various corrections and lines through things. One of the notes was: This should be an em dash.
‘What the fraggle is an em dash?’, I thought. And then class ended and I went to the bar.
A while later, we actually covered it in class, which was handy.