One way of looking at the drawing at the right is to say that it's a sketch of an Ash-throated Flycatcher eating a Monarch Butterfly. Well, let's step back and come at this a little slower. Sunlight energy travels from the sun, through space, and a tiny fraction of it showers onto the earth. An even much tinier part of that energy strikes green plants. These green plants, through the almost magical process known as photosynthesis, capture some of that energy, and store it in the chemical compound known as carbohydrate.
Energy is stored among the bonds between atoms of the carbohydrate molecule.
Anyway, calories in humankind's bread, macaroni, sauerkraut, beans, apples, and bananas are measurements of energy that not long ago was flowing through space as sunlight. In the forest, squirrels eating acorns are taking sunlight energy from oak trees. I'm sure you're getting the picture by now. Of course, animals don't keep their taken-in energy forever. Sometimes short-circuits and loops occur in the energy pathway just describe.