In the English language, there are three types of dashes with slightly different lengths: hyphen (-), en dash (–), and em dash (—). The each serve different purposes in writing.
Hyphens are used for forming compound words. They are usually used with words that, when tied, become a single concept. Some examples of hyphen use are: check-in, state-of-the-art.
A hyphen is also used when two or more words are used as an adjective before a noun. For example, “a thirty-three-year-old woman.”
En Dash (–)
En dashes are use to specify a range of dates, numbers, or time. An en dash is used with Monday-Friday, or January-December, or pages 13-72. However, if you introduce the range with from or to, do not use an en dash. For example, it is correct to either use “2010-2013 were excellent years for our grapes” or, “Our grapes grew exceptionally well from 2010 to 2013,” but not “We had good harvests from 2010-2013.”
Another use of the en dash is to report scores or contest results, such as “we won the game 10-7.” It is also used to represent direction, as in “the Chicago-Atlanta flight,” or “the east-west railway line.”
Em Dash (—)
The em dash has many uses. Two em dashes can be used instead of commas in a sentence, to provide a more emphatic tone.
Two em dashes can also replace a pair of parentheses, for a less formal and less subtle tone. Similarly, an em dash can replace a colon to provide extra emphasis on the end of the sentence.
Em dashes can also be used as bullet points in a list format.