Clicking the List Management icon 
opens the list management editor.
Every Custom Field can have a drop-down list associated with it. A list restricts possible entries in the custom field to those in the list. If there is no list associated, the field is open for users to enter information as they see fit. If it is important to control what is entered, a list needs to be associated with the custom field.
For example, it may be important to have a list in a situation where information for an MRP system is going to be extracted from Assembly Planner. This would restrict the user to information that is correct and usable by the MRP system. However, a list would typically not be appropriate for something like the description of activities on an assembly line. In this case, it would be important to give users the freedom to enter information without a list.
There are two areas of interest in the List Management editor, the first of which is the List Area.
The second area is the List Values area
List Values
List
•Select List is where you choose the list you want to view or edit.
•DataType displays the type that was selected when the list was created. This cannot be changed after creating the list. The data type of the list and the custom field it modifies should be the same. Possible data types include string (for text), integer (for numeric lists), double (also for numeric lists) and date/time.
•Sort By Value can be modified using the Edit button. When selected, the List Values will be sorted in ascending order.
•The Add button creates a new list. Specify the List Name and Data Type and whether or not the list should be sorted by value. The List Name and Sort By Value can be changed later, but the Data Type cannot be edited.
Add List Details
•Delete allows a list to be removed. Assembly Planner will ask if you want to delete the list.
•Edit lets you make changes to the List Name or change the Sort By Value setting. However, the Data Type cannot be changed after creating a list.
List Values
The List Values section of the List Management editor is laid out like a spreadsheet. Entries in the List Value column are what you will see in the drop-down list of a custom field. There is also a Description column with space for a more detailed explanation of the list value. Changes are made in the spreadsheet section by selecting the correct list from the List drop-down and clicking the Edit button at the bottom of the screen. To keep the changes made, click Save. To discard the changes, click Cancel.
For a tutorial on creating and associating a list, see the tutorials, Create Lists and Associate Lists.