OK. I was bit by that stupid '10-minutes to edit' rule.
I see from your other post that you are not going to use a 2004R. If you are working with a 4L60E, then read this post. It's basically the same as above but geared towards the 4L60E.
The servo is quite simply a hydraulic piston that applies the 2-4 band. The band is wrapped around the reverse input drum and when it's applied, it stops the drum from rotating.
If your Camaro was originally a V8 car then you already have the 'Corvette' servo. If it is a V6 transmission, then you'll want to upgrade.
The stock V8 servo is adequate for most applications that run well into the 12s. When you have enough power to push your car into the 11's and beyond, the additional clamping force generated by a larger aftermarket servo (and increased line pressure from a valve body kit) can keep your 1-2 shift sharp and extend band life.
Additionally, for any performance level, I'd recommend that you use the extra-wide Red Eagle band now available from many vendors.
