Energy is a quantity that gives an object the ability to affect other objects. There are different kinds of energy. Kinetic energy is the energy of motion, stored within a moving object. Potential energy is stored in the force between objects, perhaps in the stretch of a spring. Thermal energy can be stored in the temperature of an object.
Energy passes from place to place, object to object, but never disappears.
The total energy of the universe remains constant. Fuel is a material that has energy stored in its chemical structure. This released energy can become heat and cause the temperature of something to rise. The released energy can become the kinetic energy of a car. It can become the energy carried by sound to your ears.