I was a bit like you when I hadn't built a computer before, I was really scared that I would stuff things up.
believe me, building a computer is actually easy, you just need a little bit of knowledge and common sense
here is a guide to firewire setup
to show you where the plugs go
pretty much all the plugs can be placed using trial and error though, except for the main power plugs, none of them really put through enough power to do damage. USB and firewire are an exception becuse they are designed to be able to power devices, so there are a couple of plugs with higher volts (but only the ones coming from