Kart brakes are essential and required on all racing karts. On an oval kart, they may never have to be replaced. On a sprint kart, they may be more heavily used and need replacing.
In most karting, they have a single disc brake on the rear axle, and brake pads that are controlled with hydraulic fluid from the brake pedal to the brakes.
Rear Disc Brake System
This is the most common single disc rear brake system. It is usually mounted on the left rear.
The brake pedal is attached to the lever on top of the Master Cylinder where the hydraulic oil is put. When the brake pedal is pushed down, it forces the oil through the brake lines to the caliper assembly with the brake pads, where it forces the brake pads to squeeze the brake disc.
Front Braking work the same way, they are just on the front wheels. These are used on some of the faster shifter karts on sprint tracks, as they need maximum braking ability to navigate tight corners. A four wheel disc braking system is much better than just one rear brake. It would be overkill on an oval kart though.
Brakes sometimes get overlooked, especially on oval karts as they are hardly ever needed. Just make sure to always give them a few quick checks every week at least just to make sure they are working, because if they aren't there when you need them..It won't be pretty.