Updated: Jul 30, 2019
I'll try to sum this up as simply as possible (if you would like a full, jargon-littered biology lecture, feel free to email me).
Photosynthesis utilizes the energy of sunlight to transfer electrons from water (H2O) into carbon dioxide (CO2) in order to create carbohydrates. These carbohydrates are the food for trees.
As a bonus, our newest apprentice wrote a Haiku:
A changing of light to life
The growth continues