The entity list menu is the root menu from which you can select mobs (and other entities) that will drop an item. It should look like this:

The menu consist out of the cancel button and a list of entities.

Clicking on an entity name will select that entity and bring you back to the Mob Drop Menu and the menu will display what entity you have chosen. Some entities have a minecraft verison behind them in brackets, this indicates that the item set will only work on the minecraft version indicated, or above.