Okay...so i have had my 580ex II for a little while now and having fun with it! (although i think it is faulty as it doesn't always fire (on camera) i can fire 3 shots and the flash fire once and sometimes not at all...but i have been told to try it on another camera to see if there is something wrong there so will try that) Anyway thats not my question.
Once i have that sorted..i would like to experiment with off camera flash.

I have heard alot of people mention pocket wizards? Can somone please explain to me is that what i would get? adn where can i buy one? I looked on a few website where i have bought lenses etc but can't seem to fins anything that's called that.?
I'm assuming that they are like a wirless trigger are they? so it still goes off when you fire a shot? or is it a bit more complicated than that>? are they hard/simple to use? Also I have been looking at the different diffuser's etc that you can get but really not sure which way to go? Any links to where i can purchase these things and what i should get would be a real help.

I mainly want to experiment with portraits...different lighting angles etc..and i've seen how people take photo;s when its quite like but looks dark and uses the flash to light them up and stopping down. so yeh basically i just want to experient! hehe

Thank you for your help and advice!