You have two way to add options to dropbox fields.
If you select the "Data stored in Adsmanager" option,
you can fill the empty fields below in order to add
options to the dropbox field.
Clicking on the 'Add a value' button will add new empty
fields.
If you select the "Data stored in an external table", you
just have to specify into which database table and columns.
The options list of the dropbox field will be filled with
the content of the table.