We will discuss here about energy.
We have seen in a rail shed or shipyard that huge cranes are engaged there in lifting very heavy articles and placing those articles to somewhere else. Similarly, we might have followed a small ant carrying a piece of food in its jaws, which is much heavier than the ant weighs itself. In both the cases some works are associated with and to perform this work, be it a huge machine or a tiny ant, it needs energy. So we can treat energy as an ability to do some work or an ability to make things happen. A machine gets the energy from fuel and a living organism gets it from food.
When you switch on a light, it glows. Here electrical energy is transformed into light energy. If we rub our palms against each other for a while, we w0ould feel hot. Here heat energy is generated from mechanical energy. From here we conclude that energy cannot be produced, it may only be transformed from one form to other.
In general, energy can be divided into seven forms. They are heat, light, sound, magnetic, electrical, mechanical, and chemical. But now we will discuss about the few forms of energy (i.e. solar energy, electrical energy and magnetic energy) and their usage.