So, how do I do it? And what do I need to get? Whatever I need to get, can I get a cheap version off ebay? Is this where 'hot shoe' something comes into it? See, I really have no idea, I'm just a bit fascinated thats all. I have a sigma 530 ST flash that I have only ever used on my camera before... Would like to try more portrait stuff eventually so I guess I'll need to know about this kind of stuff

Any help would be greatly appreciated!