Rules for using DASH:
An endash (–) is used to connect numbers or to connect elements of a compound adjective: 1868–1878, Dublin–Cork trains.
The emdash (—) is twice as long as the endash. It is used to:
1. Indicate a break in thought or sentence structure
2. Introduce a phrase added for emphasis, definition, or explanation
3. Separate two clauses
I used to be indecisive—but now I’m not so sure.
– (On Mac Keyboard: Opt and minus)
— (On Mac Keyboard: Shift and Opt and minus)