The underside of plants have little, tiny openings called stomata that take in CO2, (what humans, cows, and kangaroos exhale). The CO2, sunlight and water are used by the plant to create a process called photosynthesis. Plants use photosynthesis to create their food, (carbohydrates), from CO2, sunlight, and water. Water is taken up by the roots, sunlight hits the leaves, and the stomata brings in the CO2.
The stomata is also where the plants give out oxygen, (what humans, cows, and kangaroos breathe).
Water, air, and nutrients are absorbed by the root system of the plant. The roots also act as an anchor to firmly hold the plant in place. There are tiny little hairs that come out of the roots that allow even more of the these basics to be absorbed.
Amino Acids help with this photosynthesis. You can get it in powdered from from Kelp4less. Not very expensive but very beneficial for your plants.