Photosynthesis is very complex process, and for the sake of convenience and ease of understanding, plant biologists divide it into two stages.
In the first stage, i.e. the light-dependent reaction, the chloroplast traps light and converts it into chemical energy contained in nicotine-amide adenine di-nucleotide phosphate (NADPH) and adenosine tri-phosphate (ATP), two molecules used in the second stage of photosynthesis.
In the second stage, called the light dependent reaction (formerly called the dark reaction), NADPH provides the hydrogen atoms that helps form glucose, and ATP provides the energy for this and other reactions used to synthesize glucose.
These two stages reflect the literal meaning of the term photosynthesis, to build with light energy.