This feature will "remember" the city and state that is associated with a zip code. After you have entered a new zip code/city/state combination, the system will remember it and for future entries you will only need to enter the zip code. The city and state will automatically fill in based on the entered zip code.
Zip code fields that are associated with the Auto Fill feature are shaded a slightly different color than other fields around them.
Zip codes and their associated city/state combinations can be viewed and maintained in the Waiting List Module under Settings>>Zip Code Maintenance.