The food chain which consists of all organisms has each of them placed at a specific level. The level at which an organism is placed in the food chain is called the trophic level.
At the lowest trophic level are placed pants and fungi which have the capacity to absorb energy directly from the Sun and use it to convert nutrients into biomass. Above the plants are placed the herbivores which feed on plant and obtain their energy by digesting plat matter. Carnivores are placed above the herbivores as they feed on the herbivores. There can be one or more levels of carnivores in the food chain, which the carnivores at the tertiary level feeding on those at the primary level.
A food chain generally can be considered to have 3 - 4 trophic levels.