Let's start with the rolling wheel. How do your brakes stop it?
Connected to the wheel is the rotor. That's the part of the wheel that the brake will press on to stop it from rolling.
The brake pad is the part of the brake that touches the rotor. Brake pads cause friction against the rotor, which is what stops the spinning wheel. They wear out from this friction over time, and are meant to be replaced regularly.
Brake pads are attached to the caliper, which is the part of the brake that applies the pressure. It's sort of like an arm.
The caliper works by hydraulics. The hydraulics are a series of hoses filled with brake fluid. You press on the brake pedal with the force of your foot, and the hydraulics multiply that pressure enough to stop a speeding car. The hydraulic brake fluid makes the brake pads close on the rotor to stop the car.