Delivery Methods are the ways in which you want to offer order fulfillment. This can depend on a few factors like whether you print tickets or have assigned seating, but mostly comes down to what you would like the patron to do when they come to see the show.
If you are a small company with just a check-in at the box office to get a program, then Receipt Only is usually sufficient for your operations.
Regardless of which methods of fulfillment you offer, you want to make sure that you are offering at least one way the order can be fulfilled, otherwise it won't be able to be placed.
Usually, you will only need to put numbers in those availability boxes if you are planning to switch from one delivery method to another at a certain cutoff point. (Most common is something like having a hard ticket mailing delivery method stop a couple weeks before a performance and then switching to a will call delivery method.)
With just one method of fulfillment, you want to leave those blank.