Grass is a producer, it gets eaten by the rat.
That's a primary consumer that gets eaten by the cat.
The cat's a secondary consumer, and when it rolls over and dies
It gets decomposed by bacteria and flies, yeehaw!

Producers are homotrophs, they make food of their own.
Consumers must eat producers, they can't survive alone!
Decomposers eat consumers as soon as they meet their death
And scavengers come around and they eat what's left!

Symbiosis is when two lifeforms work with eachother.
Mutualism, both benifit, like brother and brother
Parasitism, one benifits while the other does condemn,
And Comensalism, one benifits while the other, nothing happens to them!