Em-dash: use this for sentence interjections and sentence enders; can be used to replace colon. Wide as capital ‘M.’ Get there in Word with –. Can use or not use a space before and after. I like using the space. Or ctrl + alt + minus sign.

• The last time I saw him I asked him if he still believed — as he once had written — that we are at the is moment participating in one of the very greatest leaps…
• On July 22, the company was awarded the largest privatization contract ever for a prison — a 2,048-bed minimum-security facility in Taft, CA.

En-dash: half width of Em. Used to show range. Ctrl + minus in word. Often equivalent to to or versus. Width of “N.” Often represented with hyphen.

• the 1914-1918 war
• the nature-nurture debate

Hyphen: if two or more consecutive words make sense only when understood together as an adjective modifying a noun that follows, those words (excluding the noun) should be hyphenated. So special-interest money, but not special interest. Credit card  vs. credit-card application.