A dash is used to emphasise what follows.
Use dashes sparingly: not more than a pair per sentences in informal writing and (if possible) not more than a pair per paragraph in formal writing.
Some computer programs cannot display dashes (–). In this case, type two hyphens (--).
There is no blank before or after a dash in English.
Dashes for Change of Topic or Structure
Use a dash for a change of topic within a sentence.
Example: This is very important–are you listening to me?
Use a dash if the information that follows is surprising and unexpected.
Example: We went shopping in London–and met Robbie Williams.
Dashes in Dialogues
Use a dash to show hesitation.
Example: I–I–I don't know.
Dashes in Summaries and Additional Information
Use a dash to indicate a summarising clause.
Example: Jane, Daniel, Susan and I–we all were taken aback.
Use a dash to indicate an emphasised addition.
Beispiel: He prayed to his God–to Allah.
Use a dash to enclose emphasised additional information which interrupts the normal progression of the sentence.
Example: He wanted us–Caron, Susan and me–to meet his family.
Depending on the importance attached to it, additional information can be enclosed in brackets, commas or dashes.
Brackets - not important
Connor (Amy's boyfriend) bought the tickets.
Commas - neutral
Connor, Amy's boyfriend, bought the tickets.
Dashes - emphasised
Connor–Amy's boyfriend–bought the tickets.
see also: → Additional Information in Brackets
see also: → Additional Information in Commas