I haven't done a whole lot of work with flash in the past, but I'm interested in exploring the option a bit, especially for portraiture work where I need to isolate movement in less than ideal lighting.

My question is, and forgive me if this seems like a juvenile question for those of you with experience, how exactly does one determine exposure and flash power when shooting entirely analog?

I have a Canon 580EX-II flash gun right now, and I'm going to set up a small mini-studio in my new apartment next month, for which I'd like to get a strobe or two, but I'm completely lost in terms of metering for this. Can someone help me out and/or point to some resources which may be helpful?

Thanks, and sorry if this has been discussed before; I searched but couldn't find anything.