Friction produces thermal energy, also known as heat. When two surfaces rub against each other, the resistance they encounter generates heat. This happens because the kinetic energy from the moving objects is converted into thermal energy due to the friction between them.
For example, when you rub your hands together quickly, they feel warm. This warmth is the result of friction converting the kinetic energy of your moving hands into thermal energy. Similarly, when car brakes are applied, the friction between the brake pads and the wheels generates heat, which is why brakes can get very hot after prolonged use.
In summary, friction is a force that opposes motion, and in doing so, it converts kinetic energy into thermal energy, producing heat as a result.