Those are the bleeder screws. The easiest way to bleed those brakes is with a gravity brake bleeder. Or can do a bottle and put in the top of the master cylinder.
First need to make sure the brake pucks are pushed against the brake pads. I do this by using my brake bleeder attached to the MC. with the valve closed I pushed the brake pedal then open the valve. The fluid will then run back into the bleeder and then I would take out the screws in the caliper (bleed screws) and let the fluid drip out until bubbles stop.
The karts with springs on the brakes you cant pump bleed them like you do cars. You push on the brake let the fluid out, tighten the bleed screws let off the brake you will make a vacuum in the brake system and pull the pistons off the pads. (with spring return brakes)