Photosynthesis is a process of the plant absorbing the sun raze and the water and transforming it into chemical so they can live a produce oxygen for us to live.
During the day the tree absorbs CO2 and makes it into energy and sugars. During the night they use the sugars and energy to keep the plant living because there is no sunliught.
The Calvin Cycle uses the CO2 to go through all the steps in the cycle and during those steps the cycle breaks down the CO2 and and splits it up so the cycle just gets the carbon and transfer the carbon to the light dependent. while the carbon is being transfer the oxygen leaves the plant and is in the air for all the living things breath.
The light dependent reaction use the carbon and turns into ATP and then the ATP go back into the clavin cycle and then the clavin cycle turns it into NDAP+ then after all that the plant stores it and uses it for later when the sun isn't out.