I have noticed that some native english speakers use the "-" sign to explain some additional things in a sentence: eg
Sophie is going to the shop - which happened to be around the corner - to buy some groceries.
Before knowing this notation I would write the same sentence as follows:
Sophie is going to the shop, which happened to be around the corner, to buy some groceries.
To me the "-"-sign seems much clearer than a comma. Am I using the "-" correctly. If so what is the difference between a "," and a "-".