The cell takes its energy source, converts it into NADH and ATP, and then uses them to perform needed tasks in the cell. It is amazing to consider that given the diversity of life on this planet that we all use the same energy carriers. Hydrogen is the smallest element. It has one proton in its nucleus and one electron orbiting it. If you remove that electron, you have a hydrogen ion, which is also called a proton since that is all that's left.
Protons play a major role in respiration and many enzymatic reactions.
This stored up energy then drives other reactions that help the cell grow and reproduce.