There are two processes involved in photosynthesis, which are the light-dependent reactions, and the light-independent reactions. Despite its name, however, the light-independent reactions are in fact indirectly dependent on light.
As their name implies, the light-dependent reactions are dependent on light. Basically, light strikes a light harvesting complex which releases an electron. This electron is eventually passed to a chlorophyll a molecule, which reduces a primary electron acceptor, which starts several more reactions. These reactions produce O2, NADPH, and ATP.
Next comes the light-independent reactions, or the Calvin cycle. First, CO2 is attached to ribulose biphosphate, or RuBp. The resulting molecule is unstable, and breaks in two, forming two molecules of 3-phosphoglycerate, or PGA. ATP adds a phosphate group to each PGA molecule, creating glyceraldehyde 3-phosphate (G3P), which is further refined into sugar and carbohydrates.
The Calvin cycle produces sugar and carbohydrates, but it requires other molecules for it to work. It needs O2, NADPH, and ATP, all of which are supplied by the light-dependent reactions. So the Calvin cycle is dependent on the light-dependent reactions.