What is the nature of energy and how is it conversed?

Energy can be defined as the capacity to do work.

Energy can be classified into two types: potential energy, the energy an object has because of its relative position, composition, or condition, and kinetic energy, the energy that an object possesses because of its motion.

The law of conservation of energy states that the total energy of an isolated system remains constant.

Energy changes only when a force is acted upon the system. In an isolated system, no forces are acted upon that system. So, energy is conserved.