Whenever an object is caused to move, whether from a standstill or while already in motion, a Force is required. Gravity is a Universal Force. The moon orbiting the Earth. Every object in the universe exerts a force on every other object, and that force is Gravity. Friction is a Force that opposes motion.
Friction occurs when two substances rub together.
Heat is a byproduct of Friction. The motion of objects is reduced because of Friction. Why you stop swing on a swing, why a ball stops rolling. Friction can be reduced by smoothing and polishing the surface of contact, by lubricating surfaces with grease or oil, or by using roller instead of sliding. When using the brakes on a bike or car, we are increasing friction in order to stop.