ok this is the short version. shingles is caused by varicalla zoster, the virus that also causes chicken pox. what happens is that this bastard bug lives indefinitely in your spinal fluid. if you are stressed, have a low immune system and all that, then the virus can migrate along one of the spinal nerves and manifest in that characteristic, pustular (pus basically...yum) rash along the area that that particular nerve controls. this is why you usually only get it on one side of your body, and the doctor will usually know straight away what it is.
because it is along a nerve, you often get long term nerve damage, meaning that you will feel pain even though there is no injury, sometimes up to years after the infection. the soner you treat the virus, the lower the chance of this happening. the rash usually resolves by itself anyway.
if you do get nerve damage then of course it depends on how bad it is, but you might be on pain killers for a long long time afterwards, anything from paracetamol (acetominopphen for the yank annoying alternate spelling bastards) to opiate based drugs
um, thats it, really.