Hyphen, en-dashes, and em-dashes are very similar, commonly-confused pieces of punctuation.
A hyphen is used to join two words. There should be no spaces on either side of a hyphen.
A well-read book
A dark-blue sea
An en-dash is used to indicate a break, where a comma or semi colon may possibly be used instead. It’s generally a bit less formal. These are called parenthetical en-dashes. There should be a space on either side of a parenthetical en-dash.
Wait – stop!
En-dashes can also be used to show a range of numbers, or to otherwise replace the word ‘to’. In this case, there shouldn’t be a space on either side of the en-dash.
If you use an en-dash in this way, it shouldn’t be combined with ‘from’.
Correct: The Glasgow–Edinburgh train or The train from Glasgow to Edinburgh
Incorrect: The train from Glasgow–Edinburgh
Correct: Responders aged 18–24 or Responders aged from 18 to 24
Incorrect: Responders aged from 18–24
An em dash can be used to show a change in thought. In practice, em dashes have generally fallen out of use. They can be seen more often in Victorian literature.
I think that — is that the phone ringing?