You then store the glucose in your liver, which regulates how much glucose it releases into your blood stream. Your brain, muscles, and all your organs use glucose for the energy they need to do the things they do. Your muscles, etc. can also burn fat and protein for energy, but your brain must have a healthy supply of glucose, or you will die. Fortunately, plants are the best source for glucose, particularly in the form of starch. You get tons of starch in grains such as rice, wheat, and corn.
Potatoes are little bundles of starch as well.
When you eat protein, you break it up into little pieces called amino acids, and then you reassemble these into the different proteins you need. Plants need enzymes and proteins like you do, so there is protein in very cell of a plant. However, plants don't have muscles like animals do, and your muscles need lots of protein. The part of a plant that has the most protein for you to eat and build muscle with is the seed or bean. There is lots of protein in the nuts, beans, and seeds, because the plant puts it there so that the baby plant can have plenty of protein as it starts growing.