Galvanic cell using NaCl, Cu and Zn, why does it work?
I want you to try and work out the details yourself, but there's one aspect of this kind of cell that's not straightforward. At one electrode, you have a reduction reaction and at the other, an oxidation, just like any other galvanic cell. In the oxidation reaction, one of the metal electrodes is oxidized to put cations in solution. (think about which metal is more easily oxidized) In the type of galvanic cell that you may be more familiar with, a metal cation in solution is reduced onto the other electrode, but in this case, the only metal cation is $\ce{Na+}$, which is extremely difficult to reduce. Therefore, some other reduction reaction must be happening. The only other reducible substance present is water.

The two reactions occurring can be found on this table, and using the potentials in the table, you should be able to work out which reactions are occurring and at which electrodes.