Here is another entry about punctuation marks in English. If you are curious about this subject, you may be interested in the fact that the punctuation now used with English is derived from the one used with Greek and Latin. Maybe I could write another article about it, but now let’s read about the dash.
A Dash (—) is especially used to indicate a break in the thought or structure of a sentence:
‘If you work more than eleven hours a day, you have an increased risk of heart attack, according to research published last week — so perhaps the old adage, “hard work won’t kill you” isn’t as true as we thought.’
It is used in front of a list or explanation:
‘You need some ingredients to make scones — salt, butter, caster sugar, milk, self raising flour and eggs.’
After and in front of a group of words or a clause which adds something to the main sentence but could be removed:
‘The only trick — if that’s the right word — is that he is not doing it alone.’
In front of an adjunct, clause, or other group of words, for emphasis:
‘Oh Jane, this is great — really it is.’
Note that a dash is written after and before a space.