Energy can’t be made or unmade. If one object loses energy, another object will gain that energy. Energy can be converted into different forms; like how a hairdryer turns energy into heat.
When an object’s movement changes, its energy changes too. If a car slows down, it loses kinetic energy. That energy will then be changed into another type of energy like thermal energy.
When a force acts on an object, the energy of that object changes. For example, when you hit the brakes on a car, you’re applying a force to the wheels. That force converts the kinetic energy into heat.