All living things need energy to perform their life processes. how and where do they get the energy that they need ?

This related to producers and consumers, which is part of the food cycle. It is known that food are the molecules that feed living things the energy they need to move and function in metabolism. Producers such as plants or algae naturally produce their own energy and don't have to feed off other living organisms. Consumers don't naturally produce their own energy to feed off, therefore they have to consume other organisms.

carbon, hydrogen and oxygen