How does a saltwater battery work? Specifics!!!?

Im making a salt water battery for a project and need to know exactly how it works. I know that electrodes oxidize, and the difference in charge causes an electron flow, but i need to know the exact reaction that takes place between the electrodes and the electrolyte. I will be using carbon rods and galvanised screws(zinc) in salt water. Any explanation would be helpful!!! thanks