If the disc-brake cable is too loose ( disc-brake does not react immediately by pulling the barend-lever)
you can shorten the cable tension by turning the screw
A
counterclockwise. Or you unscrew screw B and
tighten the brake cable.
If your brake pad is worn-out or you want to adjust the relation between disc rotor and discbrake pad,
you can turn the screw inside the discbrake (shows towards the spokes) clockwise or counterclockwise.
The right brakepad will move toward the discrotor or away from it.