In Call of Duty: Modern Warfare III Zombies, you'll be traversing the entire region to complete missions, fight hordes of zombies and groups of enemy mercs, and progress your way to the center of the map to take down the most dangerous enemies MWZ has to offer.
A popular strategy is to run around in circles in a large area until all of the zombies are behind you, then shoot what ever bullets you have into the horde. When you run out of ammo, switch to a thundergun, or a ray gun to clear the horde.