Plants (and certain other organisms) can change the energy of the sun into food via photosynthesis. Photo means light, and synthesis means the creation of something, therefore the word means the creation of something via light. That something is energy.
In basic terms, light hits the leaf, causing electrons to be energized, which begins a chain reaction that yields energy.
For photosynthesis to occur, plants need water and carbon dioxide. They produce glucose (a type of sugar) and oxygen. The chemical equation for photosynthesis 6CO2 + 6H2O ----> (yields, in the presence of sunlight) C6H12O6 + 6O2.
