As a university co-op student, working as a proofreader at Harlequin, I was indoctrinated into the Chicago Manual of Style; since then, I have considered it my punctuation bible. In case this article does not quench your thirst for understanding the nuances of dashes, here’s a Chicago Manual of Style Article on Dashes.
There are 3 types of dashes:
(Note the absence of spaces around these dashes.)
In typesetting, a line as wide as the letter ‘m’.
Used to separate parts of a sentence (rather like parentheses).
Looks like this—sitting within a sentence—to separate parts.
In HTML: —
In typesetting, a line as wide as the letter ‘n’.
Used to connect things related by distance, like dates and numbers:
In HTML: –
A very short little line.
Sometimes incorporates spaces, depending on the situation.
Used to connect very closely related things, like compound words or when two words work together to modify a noun:
A blue-green colour.
Have a great rest-of-the-week!
In HTML: – (on the keyboard, same as a minus sign)