The process of metabolism allows the breakdown of food and the formation of the cells of living beings. Metabolism consists of two processes: catabolism and anabolism.
In the process of catabolism, the food that we eat is broken down into simpler molecules along with the release of energy in the form of ATP (adenosine triphosphate) molecules. Depending on whether the catabolism takes place in the presence of air (aerobically) or the absence of air (anaerobically), the process output and energy output will be different.
In the process of anabolism, the cells in the living beings use the products of catabolism (including energy) to form molecules of different types (from the simplest to the most complex), as per the needs of the living being. The simple molecules may include water and relatively simple salts, while the complex molecules may include DNA, RNA, carbohydrates, etc.