Grass to fox to soil
Sunlight feeds the grass, the rabbit eats the grass, the fox eats the rabbit, and when each dies, decomposers return it to the soil for new grass. A food web traces that flow of energy from one living thing to the next.
Life is made of cells
All living things are made of cells, the smallest unit of life. In a food web, energy flows from producers (plants) to consumers (animals that eat them).
Producers first
Plants are producers: they make food from sunlight. Animals are consumers because they must eat to get energy.