Without energy, nothing can move or change or even exist. Indeed, everything that ever happens from the blink of an eyelid to the creation of a galaxy depends on energy.
Energy is really the power to make something happen.
When scientists define it as 'the capacity to do work', they mean the same thing. Energy comes in many forms, from the chemical energy locked in sugar to the mechanical energy in a moving bicycle. But it always works in two ways - energy transfer and energy conversion. Energy transfer simply means it moves from one place to another, as it does when you throw a ball or smoke rises. Energy conversion means changing from one form of energy to another.