Energy chain is the flow of energy in the food chain.
Earth get energy from the sun in the form of heat and light. which is the ultimate form of energy.
This energy is further absorbed by plants to make their food by photosynthesis. Part of this energy is also stored by the plants.
This stored energy if further gained by the other animals who eat them (like from plants to deer to lion, from plants to humans, from plants to hen to human etc)
When the plants or animal die the energy from their body again return to earth's atmosphere either to land, air or water in the form of various nutrients or minerals