A food chain always start with a producer, a organism that makes food. This is usually a green plant, because plants can make their own food using photosynthesis.
A food chain ends with a consumer, a animal that eats a plant or another animal.
For example,
Grass --> Cow --> Human
Note: the arrows in a food chain show the ways energy is moving. They do now show 'what eats what'!
Hope this helps :)
