Buying a flash: the basics?

[joanium]

Hi all. I have an Olympus E-300 and have been invited to take photos at a ball. I imagine I'll be taking photos of people in a low light situation. It might just be time for me to buy an external flash. Could you give me the basics of what to look for? Assume I know nothing about flashes!

[Saralonde]

Checkout this site. It can answer a lot of questions.
http://strobist.blogspot.com/2006/03/lighting-101.html
Also this on the blog
http://digital-photography-school.com/blog/how-to-achieve-great-indoor-photography-results/