Plants are autotrophs. This means that they can make their own food. For this reason, autotrophs are sometimes called producers. Plants use light, water, and carbon dioxide to produce oxygen and glucose through a process called photosynthesis. This process is not unique to plants, as many types of protists and bacteria are also capable of photosynthesis.
Photosynthesis is done in a cell structure called a chloroplast, and chloroplasts are typically found in the leaves of a plant. Chloroplasts contain a special pigment called chlorophyll that absorbs the light energy to fuel the entire photosynthetic process. Many students are surprised to find out that chlorophyll reflects green light rather than absorbs it. Green light is reflected out/off of the chloroplast, and that light goes into a person's eye. Consequently, the person sees green. The chlorophyll is located inside the thylakoid membrane, and the thylakoid membrane is arranged in long folds within the chloroplast. This ends up looking like a stack of quarters in electron micrographs.
The chloroplasts allow plants to produce glucose, which is a type of sugar and is useful to the plant because the plant cells still need to produce ATP energy. In order to produce ATP energy, the plant cell must do a process known as cellular respiration. Cellular respiration occurs in the mitochondria and uses the newly produced glucose along with oxygen to make ATP.