Brake pads convert the kinetic energy of the car to thermal energy by friction. In essence, the caliper clamps or squeezes the two pads together into the spinning rotor to slow/stop the vehicle. When the pad connects with the rotor, friction is created and the vehicle is brought to a stop.
Brake pads need to be replaced often and most automakers have installed an alerting method to let drivers know when it’s time for a change. Some have a thin piece of soft metal that causes the brakes to squeal when the pads are too thin, while others have a soft metal tab embedded in the pad material that closes an electric circuit and lights a warning light when the brake pad gets thin. More expensive cars may use an electronic sensor. No matter how you are alerted be sure to change those pads the instant you notice they are getting a bit dull.
When replacing your pads, check your calipers to be sure they are in good condition. If wear is detected, browse through the “Braking” section of your vehicle page to select replacements that fit your needs.