For everyone and everything, that means being able to grow and move. For babies, it means eating healthy food to develop, and for plants it means converting sunlight and water into energy to grow.
Food is stored energy.
When you eat it, your body uses it to do all kinds of work from running and jumping to thinking. We usually think of energy as doing other kinds of work. For instance, energy is used to move people from one place to another in cars or to provide light and heat in buildings. Like your body using the energy in food, we often use fuels to give us stored energy. Gasoline used to power cars is one example.