If you want a column to have a lookup associated with it, you have to create a Control Source for this column. This Control Source will appear on the list menu that opens when the arrow button of the Lookup Source input field of the Column Details screen is pressed.
Each Control Source for a lookup consists of two columns (Code and Description) that in turn will appear in the list menus of the respective input fields after the Control Source is defined.
To map a Control Source to the corresponding column of the Main Source:
1. Select a Control source appropriate for the Main Source column you are setting up.
2. Clicking on the button of the Lookup Source Column input field opens a lookup with the list of sources (Code and Description).
NOTE: You will have to map Control Sources to the Main Source again when setting up Data Model.
NOTE: Please refer to the Appendix section for sample Control Source setup.