Flash Lighting for Photography
Check out this link to Strobist for a beginning lighting course in flash photography.
Here is a video of the quick overview that they do at the beginning of the article:
The whole lesson is broken up into many easily understood parts. They cover all the bases when it comes to using simple flash units as off camera lighting. The cover ways to mount your flash, different ways to sync (trigger) the strobe, along with accessories for shaping and placing light.