Question

What is the relation between work and energy ?
How work=energy?

Answer 1

Work can be defined as transfer of energy. In physics we say that work is done on an object when you transfer energy to that object. If one object transfers (gives) energy to a second object, then the first object does work on the second object.

Work enegy principle

There is a strong connection between work and energy, in a sense that when there is a net force doing work on an object, the object's kinetic energy will change by an amount equal to the work done:

Energy is defined as the capacity to do work. Work is the force times displacement.
Work and energy have same unit. Thus work = energy