The Work of Energy

Energy: The ability of a system to do work.

According to Special Relativity energy has mass and that the mass all matter is a result of energy. E = mc²² so all substance is based on energy.

The 1st Law of Thermodynamics says that energy in any interaction is conserved. That is the total amount of energy in the universe is constant. It is also stated as energy can not be created or destroyed but it can change forms.

The SI Unit for energy is the joule (J):  Newton-meters = m²·kg·s^-2

Common Types of Energy

Heat energy: The energy associated with the temperature of an object.
Light energy: The energy associated with visible light.
Electrical energy: The energy associated with an electric current.
Chemical energy: The energy associated with the reactions involving molecules.
Nuclear energy: The energy associated with reactions involving atomic nuclei.
Kinetic energy: The energy associated with motion.
Potential energy: The energy of a system based on its position or condition. Stored energy.
Rest mass energy: The energy of an object that is not in motion. E= mc²

Energy is one of the three main parts of the Universe space, time and mass and relativity shows them to be inter-related. Space and time are so interrelated that they form a single entity. Furthermore mass warps space-time forming Gravity and the motion of mass contracts both space and time. 

In conclusion in common experience energy is what moves us and allows us to move thing. Physics has shown it to be a lot more. It is a fundamental part of the universe.