Pretend you are a giant sequoia tree. You couldn't go to the store, so where would you get your food? How much would you have to eat?
Think about it? You probably would start eating everything around you.
But trees don't have to. There are no holes around trees where they dug up last nights dinner! Trees use only water, air, and the energy from the sun to make the food that gives them the energy they need to grow.
In fact, ONLY PLANTS can take the energy from the sun and pack it up into food molecules so the rest of us can run on solar power, too.
This process is called photosynthesis.
Your body is made of the elements found in the earth.
So. Do you eat dirt?
Heavens NO! But plants do.
Plants take minerals and chemicals from the ground and build themselves. When you eat the plants, your body builds itself with the building blocks that the plant took from the soil.