Whats the cam gear all about

I've ordered a CAM gear from AEM and it should be here soon but I'm not quite sure on what to do with it...I purchased it because the gears I have now are disgusting and my car is all show and some go...but could somebody please explan to me what a cam gear does and how i should "tune" or "retard" it to meet with my engine ? Thanks guys. Also are under drive pulleys a waste of money on a civic ?