Ok, this is something I’m increasingly seeing done wrong in essays, so this will just be a very quick reminder of the difference between a hyphen and a dash.
Hyphens connect words together, phrases such as face-to-face have hyphens, you can also hyphenate non-standard phrases e.g. ‘that funny head-floating-above-your-body feeling’ to show that you mean the phrase to be taken as a whole as a single entity which English does not have a singular word to describe.
Dashes separate, they can be used grammatically like commas – for example in the middle of a sentence – to break the text in the same way commas would. However, dashes by their nature (as Grammar Girl states) draw attention to the part of the sentence set aside by them. The quick and dirty difference between parenthesis, commas and dashes, as stated by Grammar Girl is the following:
Use parentheses when you want to enclose something that is incidental to the sentence, something that is background or almost unnecessary.
Use dashes when you want to enclose or set off something that deserves a lot of attention, is meant to interrupt your sentence, or already has commas or parentheses in it.
Use commas to enclose things that belong firmly in the flow of your sentence.
These are some examples of INCORRECT usage
The cats were different breeds:- Siamese, Persian and Manx.
Do not use a hyphen after a colon.
I went to a party- it was at Linda’s house- and I stayed all night.
Dashes should never connect to the surrounding text, they should have a gap either side
All I wanted was a face- to- face- talk with him.
Hyphens should always connect all the words in a phrase and should never have gaps between them.
Microsoft Word is very helpful in differentiating dashes and hyphens, when a dash is detected (because you have used the hyphen key, but left gaps either side of the hyphen) it will aromatically elongate the dash to make it more obvious, like so:
Word is rather clever – it can detect dashes because it can see the gaps. As you can see, hyphenated phrases such as face-to-face have shorter marks.