Dashes are used in three major ways (interrupted sentences, interrupted dialogue, and for emphasis). They CANNOT be used wherever you would put a comma.
How to Insert a Dash (—)
Some computers will create the dash for you if you type the hyphen (-) button twice [next to your zero and end parenthesis button on your keyboard]. If this does not work, go to the INSERT function at the top of word and click on SYMBOL. Search until you find your dash!
To separate things that interrupt in the middle of a sentence.
Three of my favorite candies— Snickers, Twix, and Three Musketeers— are made by Mars Inc.
My best friends— Jon, Katie, and Rene— are on their way now.
To show interruptions in speech dialogue. (When someone cuts you off)
Lisa said, “what if we—“
“No!” exclaimed Erica
“Why don’t we—” suggested Mary before she was interrupted.
“I have a better idea,” said Joe
To emphasize a part of a sentence. (Think of it as when your mom is telling you to do something, and her voice changes at the end to stress that you NEED to do what she is telling you… or else)
Clean your room—now.
You can drive yourself to the party—just make sure you are home on time.