ok im still new in the amps department. i got this peavy mc vt-series half stack. i've had it for awhile now. my question is. what are those other plugs in the back of the head of the amp? the only one im using is the plug that says" speaker main". and i connect that to the cab. but there's also more back there like aux, power amp in, preamp out, line out. so what are those for? do i need them?
preamp out and power amp in are your send and recieve for your effects loop.
the line out is for recording (better to mic your amp though)

No, you don't need them. You can put your effects between your guitar and your amp, but it's nice to have that option to test effects out in your loop to see if you like them there better.
Power in and Preamp out are for using effect pedals. Usually the quality will be better in the pedals are in the loop instead of before the input jack.
i c. so its the same as an effect loop. nice. cuz i wanted an effect loop. thanks guys. also. my amp also has a built in reverb. but for some reason, when i turn it up i dont hear any changes. so i guess its broken. is there a way to fix that? or do i have to bring it to a shop to get it fixed?
how do i knwo its the reverb tank? is there a label on it or something? i dont have to open up the head do i? i hope its something i can fix though.