Mutualism is when both organisms benefit from the food chain. For example, a bird gets to eat when a cow has bugs on them and allows the cow to be more comfy..
Commensalism is when only one organism benefits. For example when a plant gets energy from the sun.
Parasitism is when only one benefits and the other is harmed.For example when a bird eats a worm. the bird get to eat but the worm dies.