The process of photosynthesis starts with the sun which provides light energy that helps plants create glucose.
When added with H2O (water)…
...and CO2 (Carbon Dioxide) gathered from the surrounding air (it will enter through the stomata in the plant's leaves),
CO2 will combine with the energy stored in the plant creating glucose. Glucose is a sugar that will spread throughout the plant and help provide it the nutrients it will need to stay alive and keep growing.
This process will repeat many times.
In return, the plant will admit Oxygen allowing living beings like ourselves to breath. Other organisms that have the ability of photosynthesis would include pretty much all types of plants, bacteria, viruses and more.