A food chain is a simple way to show how energy and nutrients move through an ecosystem. It starts with producers, like plants, which make their own food using sunlight. Then, herbivores eat these plants, and carnivores eat the herbivores. Each step in the chain is called a "trophic level," and it helps us understand who eats whom in nature. For example, in a forest, grass grows and is eaten by a rabbit. The rabbit is then eaten by a fox. This chain illustrates how energy flows from one organism to another, highlighting the importance of each link in maintaining a balanced ecosystem.