When do I use a dash?

The APA Blog has two articles on using the en dash – the short dash – and when to use the longer dash —  the em dash — in your writings

The em dash is mostly used to set off a comment you want to make on the surrounding material.

 Em dash    http://blog.apastyle.org/apastyle/2010/09/computer-editing-tip-em-dashes.html 

The en dash is used for ranges, such as page ranges or dates.

En dash    http://blog.apastyle.org/apastyle/2010/09/computer-editing-tip-en-dashes.html

Both posts show you how to create the two dashes in Word.