People who are not well schooled in typography may use hyphens anywhere a dash is called for, or may even use the three different dashes interchangeably. However, each dash has its own purpose.
Hyphens are only used within or between words.
Hyphens may be used to link compound words together. Example: in-house.
Hyphens are used break words between syllables at the end of a line of text; hence the word, hyphenation.
The hyphen is the shortest dash.
The width of an en dash is half the point size of the type being used. So in a 10 point type, the en dash would be 5 points wide..
En dashes are used to indicate a range of values. 10–14 indicates the numbers 10, 11, 12, 13, and 14, for instance.
Some designers use an en dash instead of an em dash simply because they think it looks better.
You can type an en dash on a PC by using ALT + 0150 (hold down the ALT key and type in 0150 on the numeric keypad). You can type an en dash on a Mac by hitting Option + - (hold down the Option key while typing a hyphen).
The width of an em dash is the same as the point size of the type being used. So in a 10 point type, the em dash would be 10 points wide..
Em dashes can be used to set off a phrase — like this — instead of parentheses.
Em dashes can be used to show a sudden change in tone — like this.
Em dashes can be used to show a missing part of a word, as in f—k.
A well designed em dash should not touch any letters. If it does, you need to insert a thin space before and after it; do not put word spaces before and after an em dash.
You can type an em dash on a PC by using ALT + 0151 (hold down the ALT key and type in 0151 on the numeric keypad). You can type an em dash on a Mac by typing Shift + Option + -. (hold down the Shift and Option keys while typing a hyphen)