Photosynthesis is the process by which autotrophs, photosynthesizing organisms, transform the energy from light into chemical energy stored usually in sugars like glucose. It consists of two parts, the light dependent reactions and the light independent reactions.
In the light dependent reactions, light is absorbed by a pigment such as chlorophyll, and passed on through an electron transport chain where the high energy compound produced using the energy from light is successively changed to lower and lower energy compounds, creating ATP from ADP and NADPH from NADP+.
In the light independent reactions, the energetic molecules ATP and NADPH are oxidized, releasing energy which is used to create compounds such as glucose. As the name implies, these reactions can occur when it is dark out as long as the ATP and NADPH stores last. The Calvin cycle is the most commonly known the light independent reactions.