Despite the fact that this article is more punctuation oriented instead of the usual typographic theory, it should come as no surprise that both are closely related. It’s also important to realise that in order to effectively use typography it’s important that you have a solid understanding of the written language.
So this article will be focusing on something I previously knew relatively little about and is perhaps one of the most neglected and misused forms of punctuation, that is the hyphen, the en-dash and the em-dash.
“these three different marks have very different purposes, and using a hyphen to do an m-dash’s job is just as much of a punctuation error as using a question mark in place of a comma.”
–Ilene Strizver 
As Ilene states each of these marks has it’s own unique purpose, so I’m going to provide some information about each of them and show working examples of how they are intended to be implimented.
Hyphens are the shortest dash of the three and it can be located on your keyboard, next to the zero key. They are used to break words at the end of a line, to help reduce the rag in a body of text, which is the uneven vertical space. This is usually referred to as hyphenation.
Hyphens are also used to connect compound words, but to explain when exactly you can do this would require an entire article. Some examples of hyphenated compound words are self-serving and anti-establishment.
Hyphens also symbolise relationships and interestingly as noted on Linotypes article on this very topic, The Brown-Jones Theory (with a hyphen) and The Brown–Jones Company (with an en-dash) actually mean two different things. The first instance with a hyphen indicates one person, whereas the second instance with an en-dash indicates two people.
En-dashes are bigger than hyphens but half the size of an em-dash, you can easily remember this by the similarities between the en and em sizes in typography, which are relative measurements based on a font size.
They are used when indicating a range of values like a span of time 13:00–14:00 or Monday–Friday. You can also think of them as replacements for the words “to” and “from” and they can also be used to replace hyphens when you combine open compound words.
To get an en-dash on a mac you just need to press option + – (hyphen). On windows you can use the four digit alt code alt + 0150.
The Em-dash is the longest of the three. They can be used to represent a change or break in thought, but it’s advised to use them sparingly in formal writing. When used in informal writing however, they may replace commas, semi colons, colons and parentheses for added emphasis.
To get an em-dash on a mac you can use shift + option and – (hyphen key). On windows you can use the four digit alt code alt + 0151.
It’s the awareness of little details like this that can make the difference between good typography and great typography, because no matter how well set a piece of content looks, the credibility can be damaged if there are noticeable spelling, grammar or punctuation mistakes.
-  Ilene Strizver, n.d., Hyphens, En-dashes and Em-dashes – Fonts.com [Fonts.com], [online]. Available:http://www.fonts.com/content/learning /fyti/glyphs/hyphens-and-dashes [13/08/2013].
-  undefined, 09/05/2005, Compound Words: When to Hyphenate [Get it Write Online], [online]. Available:http://www.getitwriteonline.com/archive/ 042703compwdshyph.htm [13/08/2013].
-  Monotype GmbH, email@example.com, 01/10/2006, Learn about Type – Akira says … , [online]. Available:http://www.linotype.com/2705-20904/ hyphensendashesandemdashes.html [13/08/2013].
- Phillip Patterson, 31/07/2013, Line Lengths & Measures [Type & Music], [online]. Available: http://typeandmusic.com/line-lengths-measures/[13/08/2013].
-  Jane Straus, n.d., Dashes | Punctuation Rules | Em Dash | En Dash [Grammar and Punctuation | The Blue Book of Grammar and Punctuation], [online]. Available:http://www.grammarbook.com/ punctuation/dashes.asp [13/08/2013].