Our universe is made up of 2 things that is matter and energy. It is pretty easy to understand the concept of matter because anything which occupy space and has a mass can be defined as matter. When you try to understand energy, it is much more complex.
If you go according to the technical definition of energy, energy can be defined as the ability to move things or to do any kind of work. You can exclaim that energy is the ability of anything to do a certain type of work.
The law of conservation of energy also states that, energy can neither be created nor destroyed; it can be only converted from one form to another. This means that whenever you are speaking about the generation of energy, you are actually speaking about the conversion of energy from one form to another.
In most of the cases, where it might seem that energy is getting created from scratch, the principal is that energy is being converted from potential energy which was already inside the object which is being used to generate the energy.
Energy is not just confined to a couple of different forms of energy. If you look into the variety of options for energy, you would realise that it can be in the form of kinetic energy or it can be in the form of potential energy or it can be in the electrical or chemical or thermal form. Therefore, you can use this energy in the form in which it exists or you can use the energy by converting it into some other form.
The conversion of energy can be done easily by a proper mechanism.
Electricity generation plants like geothermal power plant, hydroelectricity power plant make the usage of conversion of energy to generate electricity. Moreover, when you are speaking about solar electricity, the light energy is converted again into electricity for your usage.
What is Energy in Short
So, as you can see in each and every application of energy, it is converted from one form to the form in which it can be easily used. The renewable forms of energy are present in abundant and therefore you can use them quite easily but if you are speaking about the non-renewable forms of energy like fossil fuels, they are limited in nature and therefore at some point of time they would be extinct. The whole world is moving from non-renewable forms of energy to renewable forms of energy to ensure a constant supply throughout the generations