what exactly would it do...

...right now, my car is intermittently turning on (I've had a lot of work done in the past few weeks, but this problem is bugging me)! Sometimes when I try to start the car, nothing (not even a click, no CEL's either), except all my accessories work just fine...stereo hits hard, lights don't dim...could this be the starter relay?

Here is what has been done in the past few weeks-
New spark plugs
New spark plug wires MSD
New ignition coil MSD
New starter
New battery Blue top Optima
New timing belt & some pulleys too
New clutch & flywheel

I'm gonna' check this relay later, just wanted to know what it does exactly and give me a little headstart on what to look for...thanx everyone for all your help over the past month!!!:thumbsup LONG LIVE 2GNT.com!!!

Could be the relay, check the cables on the starter to be sure they are tight, and be sure the thick ground wire that is supposed to be bolted to one of the tranny-to-block bolts is there and tight. Also, check the clutch switch by the clutch pedal to be sure thats working. You can easily test taht just by unplugging it. With that unplugged, you can start the car without using the clutch pedal(so be careful its not in gear with the clutch out when you start it). Could also be the actual starter going bad.