Energy is available in nature in different forms. Some forms of energy are useful directly as it is available in nature and while some are not suitable to be used directly as available in nature.
For example, clothes or food grains are usefully dried in direct sunlight, using available sunshine (solar heat energy) in nature. During a sunny daytime, all our open air activities are naturally 'lighted' by the sun and we need no artificial lighting. Wind blows naturally.
It may be used to fly kites, move boats with sails, etc. Unfortunately, some of the naturally available forms of energy cause natural disasters if these are not controllable by human beings and of very large intensity.
Cyclones are such natural disasters, with huge energy outbreaks of moving wind. Lightning is another, with high voltage electricity flow. Any naturally available form of energy is called primary energy.
Though use of these primary energies for the benefit of mankind is not always possible, these primary energies are essentially all sorts of energies available on earth. However, according to the principle of energy conservation, one form of energy may be converted to another using a suitable developed method, with total amount of energy always being conserved.
These converted forms of energy from any primary energy are called secondary energies. Useful conversions of primary energy into secondary energy are the keys to human civilization and are considered very valuable technologies.