Animals consume these plants. We call these consumers. Another name for plant eaters is herbivore. Carnivores eat herbivores. Omnivores eat both herbivores and carnivores.
Man is an omnivore.
Energy flow in an ecosystem is one way. Much energy is lost in the form of heat. The higher the trophic level, the less energy is available to the consumer. Decomposers are an essential part of this model, also. Their primary function is to cycle nutrients.