The small animals and fish who eat plankton then become food for larger fish, such as the tuna and mackeral. These fish are then eaten by larger fish and animals, such as the shark and dolphin. Check out the menu at a seafood restaurant next time you are eating there. Don't be surprised if you find shark on the menu. The food chain on land is just as complex as in the sea.
Small animals eat plants or bugs.
Larger animals then eat them, with even larger animals eating them. We humans eat many of the plants and animals on earth. That's why we rely so heavily on all plants and animals for our existance. A break in the food chain can impact everyone. Here is a simple example of a food chain in the wild.