Biology IB student, I’ll be glad to offer some advice. Photosynthesis is a complicated thing, but it can be explained.
SiX H2O (water) is brought into the leaf and split into twelve hydrogen (H2) and six oxygen (O2 (your teacher may want you to balance the equation, which is why you need 6 h20 to produce a balanced equation.)
The splitting is done when a photon hits an organelle in the chloroplast called a thylakoid. I’m not sure if this is part of your level of bio. If not, just keep that as FYI. The hydrogens and oxygens will be used in the production of glucose.
The six CO2 molecules are brought in and split using ATP (cell energy) into 6 carbon and six oxygens. The carbon will be used in the formation of glucose, and the six remaining oxygens will be released as a byproduct. FYI, this process is a light independent reaction called the Calvin cycle.
Finally, you get glucose (C6H12O6) and oxygen (O2). Glucose is a sugar used by the plant as a way to store energy for use later, and is also the carbohydrate we eat when animals consume plants. The extra oxygen actually is not needed by the plant, and is released as a byproduct. The oxygen is needed by many other organisms, mostly animals for their cellular functions like extracting energy from that glucose.
I know it’s not the best explanation, but this is a sort of rough outline of events without going too specific into material that you may not need, like how the water and carbon dioxide split, and the intricate parts of those processes. I hope this answers your question, and good luck on your exam!