Rear brake problem

Hey all, Im new to this board and just had a quick question..

While riding in Ohio at NEMX a week back near the end of the ride my 2001 CR125 started squeaking. I just thought it was the chain, so I lubed it up but the awful squeal was still there. Upon further inspection, (I dont know much about brakes) we realized the piston thign that pushes on the pads was all the way over making the pad rub. I was told to bleed the air out of my brakes, and then to push the piston back in the cylinder and it should return by itself. I bled the air out, (just fluid?) and pushed the right pad over with a screwdriver, but once I pumped the pedal it didnt return. Whats wrong with it? The little bolt where you bleed the air out of doesnt have that little rubber thing over it..could that be the problem? Would a piece of duct tape keep it from sucking air?

Thanks alot

I dont know much about brakes, do I just remove those pins or do I have to take the whole brake apart? How do I measure the pads? Whats the minimum? What type of grease do I use? What part is actually the "caliper"