How do you use plants?
It's true that we eat plants regularly - some of us more than others. Salads, bread, even that baked potato you had for dinner the other night - they are all plant-based foods. But if you think about it a bit more, have you used plants in other ways? If you're wearing cotton clothing, yep, you're wearing something whose basic material started its life as a plant.
Over millenia, people have depended on plants for food, clothing, shelter, medicine, and even religious and ornamental purposes. Ethnobotany is the study of these purposes. It is the study of how people incorporate plants into their everyday lives.