PRO TIPS before we start:
If you're writing for publication by someone else, check their style guide for the requirements regarding these symbols. In-house style guides can vary significantly from common usage.
Consistency is what really matters. You can break a grammar or punctuation rule where you feel it's appropriate to your context, but be sure to do so without fail—Every Single Time you use it.
THE HYPHEN -
To start with:
Hyphens are not dashes. Dashes are longer: ― and –
Hyphens should never have spaces next to them.
Hyphens connect related words such as non-hyphenated and super-confused. But what if you've got some related words and you're not sure if they should be hyphenated?
Your first option is to consult a dictionary, for US English, use Merriam-Webster. This should lead you to the correct version, good-looking.
Your other option is to type your word with a hyphen and without (nitty-gritty nitty gritty) into a search engine and look for helpful articles on which is correct. That would be nitty-gritty. You may find you can join the words without using a hyphen, as with firefighter.
If you're into self-improvement, go to my post on the rules for hyphens, which gives you the good, solid facts in good, solid detail so you can make your own decisions.
Hyphens make great separators.
"My name is spelled A-M-I-R."
"The number I have is 9-3-7. It seems to be incorrect."
Hyphens create a staccato effect in speech.
Try this out for sound:
"I-I-I think we should c-c-call an ambulance."
(Ellipses give a different, more faltering effect, while em dashes signify interrupted speech. See examples of both below.)
THE EM DASH —
This is the longest dash, and in US English, it never has spaces next to it unless it's at the end of a sentence.
Using the em dash to show a sudden break or interruption in speech.
"I don't think—"
The siren went off, shrill and jarring.
In US English, faltering speech is usually denoted by an ellipsis—see below.
Em dashes can also be used in place of brackets or bracketing commas.
She started a blog, and people, complete strangers, were soon sending money.
She started a blog, and people (complete strangers) were soon sending money.
She started a blog, and people—complete strangers—were soon sending money.
The submarine was yellow, a bizarre shade of yellow.
The submarine was yellow (a bizarre shade of yellow).
The submarine was yellow—a bizarre shade of yellow.
PRO TIP 1: regardless of where in a sentence it appears, an em dash isn't followed by any punctuation unless a question mark is needed at the end of a sentence.
PRO TIP 2: Be careful not to overuse the em dash, as the interruptions it creates will start irritating your reader.
As Bryan A. Garner says in The Winning Brief:
“[I]f you learn how to use dashes well, without overdoing them,
you’ll wonder how you ever did without them.”
THE EN DASH –
This is the shorter dash, and many people think it's a hyphen, but they're wrong! The hyphen joins related words like well-intentioned and mind-numbing. The en dash is used to join numbers, letters, or words, essentially replacing words like 'through', 'until', 'and', or 'to'.
Our meeting will be from 6–8 tomorrow night.
I'll be there around 6–7.
The surnames of the first group are from A–F.
This magazine is the January–March edition.
PRO TIP: In US English, don't use the en dash as a bracket—that's the em dash!
Did you ever wonder how the dashes got their names? Well, the em dash is traditionally as long as a typewritten m, and the en dash as long as a typewritten n, hence m (em) and n (en) dashes.
THE ELLIPSIS . . .
Did you know?
The word ellipsis is singular, while ellipses is plural.
The Chicago Manual of Style (CMOS), which gives us the grammar rules for US English fiction and self-help, requires an ellipsis to have a space before it and spaces between the dots . . .
There should be a space between it and any other punctuation EXCEPT a quotation mark, an em dash, and a bracket. So, like this . . . . this . . . , this . . . ; this . . . : this . . . ? and this . . . ! The rest should look like this . . ." like this . . .— or like this . . .)
An ellipsis can be used to denote faltering speech.
"I . . . I . . . I don't like her."
Holly was afraid of what the answer might be. "Do you know if she's . . . ?"
He just vanished . . . .
Ellipses are also used in quotes where words have been left out, and if they're at the end of a sentence, they're followed by the appropriate punctuation.
"To be, or not to be . . . is the question." Hamlet, Act 3: Scene 1
Always remember, you have within you the strength, the patience, and the passion to reach for the stars . . . ." Harriet Tubman
And there you have it!