Identify the reactants, (substrate), and products of photosynthesis.

Read this: Photosynthesis - (Wikipedia)

It has all the information you need.

CO2 (Carbon Dioxide), Light from the sun and H2O (Water) are the reactants. After the reaction is complete, Oxygen and Glucose are created. In the equation below, the number '6' before each of the compounds if the number of respective molecules required for the process to be successful.

6 CO2 (Carbon Dioxide) + 6 H20 (Water) + Light → C6H12O6 (Glucose) + 6 O2 (Oxygen)

Glucose, the final product, is stored in the plant's cells while the plant throws off Oxygen into the surrounding air, benefiting humans.