If your self adjusters are not seized up, the rear brakes will adjust themselves, no need to back up and hit the brakes
If your park brake does not hold, the first thing that needs to be done is to remove the drums on both sides and make sure your brake shoes have enough lining left. If there is then you should clean and adjust the self adjusters manually. Parking brake cables rarely go far enough out of adjustment that they don't work at all. And over adjusting them will not cause the wheel cylinders to blow out and or leak, but it can cause your rear brakes to grab too quickly and possibly overheat (if they are dragging) and glaze
If you don't understand how drum brakes work, you should take it to a qualified garage. Not trying to be a jerk here but screwing up your brakes can cause bad things to happen
if you know what I mean.