the adjuster on the bottom of the rear brakes is a starwheel used to adjust the bottom end of the shoes. i usually turn this wheel enough so that when the brake drum is installed it will move freely but you can still feel some friction from the shoes. you don't want it too loose that the wheel will keep spinning, but you don't want it too tight either that the wheel only spins a 1/4 turn. this will cause too much friction and could overheat your drum and cause warping.
on the front end the caliper has one piston. the piston pushes against one side of the rotor. the piston doesn't really move, but pushes the caliper body out, in turn pulling in the pads on the other side of the rotor.
hope this helps.
i re-read your post again. on your second question, are you talking about the wheel cylinders on the back? if only one side of the cylinder is moving then it's probably buggered. you could try pushing it in a bit to see if it breaks free, but you're probably better off to replace it. they're probably only $30 or so, if that.