Photosynthesis is the process that plants use to convert the energy in sunlight into food that they use for energy. In order to carry out photosynthesis, plants need not only sunlight but also water and carbon dioxide. The food they make is called glucose, which is a simple sugar.
Photosynthesis takes place in the chloroplasts, which are organelles found in the plant's leaves. Chloroplasts contain a green pigment called chlorophyll, which is what gives plants their green color. Chlorophyll is responsible for absorbing the sunlight that begins the photosynthetic process.
Plants don't necessarily need to be in the sun the entire time they are carrying out photosynthesis. The first chemical reactions of photosynthesis, called the light reactions, occur when chlorophyll captures the sunlight and converts its energy to a chemical called ATP. The later reactions of photosynthesis, called the dark reactions, can occur without the presence of sunlight. During the dark reactions, ATP is used to make glucose.
The glucose that plants make during photosynthesis may be broken down and used for energy right away, or it may be stored for later use. Green plants store sugar by converting it to starch. Later, when the plant needs energy, this starch is broken down into glucose and used.