When you install the caliper, the banjo bolt gets fed through the end of the brake hose and mounts to the inlet of the caliper.
Brake calipers are a key component in a disc brake system. The calipers use hydraulic muscle to squeeze the brake pads against the rotors. The clamping force creates friction between the pads and rotor that slows the vehicle and brings it to a halt. If a caliper is leaking or sticking, however, it may not apply the brakes properly.