How does a simple food chain work?

A food chain describes how energy and nutrients move through an ecosystem. Energy is transferred from one living organism through another in the form of food. At the basic level there are plants that produce the energy, then it moves up to higher-level organisms like herbivores. After that when carnivores eat the herbivores, energy is transferred from one to the other.

Further Readings – 

1. Energy Flow in Ecosystem
2. Biodiversity – Species, Genetics & Ecosystem