Here's the whole idea in one breath: no living thing feeds itself alone — every one is plugged into a web of who-eats-what, and the whole thing runs on energy that started in the Sun. Pull on any one strand and you feel the rest of the web tug back.
Take a Paddock at Dusk
Stand at the edge of a paddock and look hard. The grass is quietly catching sunlight. A grasshopper is chewing the grass. A frog flicks out its tongue and takes the grasshopper. A snake swallows the frog. A hawk drops out of the sky and takes the snake. Nobody arranged this — it just is how the place works, and every one of those animals depends, a few steps back, on the grass and the Sun. Take the grass away and the whole line starves from the bottom up.
The One Secret: Energy Flows from the Sun, Through Producers, to Consumers
Zoom out and the messy paddock turns tidy. The Sun pours energy in. Producers — the green plants — are the only ones who can capture it directly, turning sunlight into food through photosynthesis. Everything else is a consumer: it can't make its own food, so it has to eat. A grasshopper eats the producer; a frog eats the grasshopper; a hawk eats higher up still. Energy gets handed along the line, meal by meal.
A single line like grass → grasshopper → frog → snake → hawk is a food chain. But real life is never one neat line — the frog eats more than grasshoppers, the hawk eats more than snakes. Link all those chains together and you get a food web: dozens of chains crisscrossing, every species tied to several others.
One thing trips everyone, so look at it now: the arrows point in the direction the energy flows — from the thing being eaten to the thing eating it. Grass → grasshopper, because the energy moves from grass into the grasshopper. The arrow always aims at the eater, never at the food. Draw a few in the toy and let it check you — getting the arrows right is half of reading any web.