This is where you tell PizzaBoy which app(s) you are working for. Every delivery in PizzaBoy must be tagged with an app. To save space around the app, PizzaBoy will frequently just show the abbreviation. So, for example, if you began to deliver for Caviar, you might make its abbreviation CV.
The “Order” refers to the order in which apps will appear in various pop-up menus. You should renumber the apps so that the one you use the most is #1. That will save you time while entering your deliveries each day.