As part of the installation it also adds two icons to the Navigate Tab on the Sales Order Ribbon, Document Promotion Codes and Promotion Summary.
The Document Promotion Codes action allows you to see which previously created promotion codes, have been applied to the Sales document using the Apply Promotion button.
To use Promotion Codes, go to the ribbon on the Navigate Tab and choose Document Promotion Codes. Here, enter the codes in the edit screen.
Once the code is entered, click to move off the line, then click the cross to close that edit screen. The code is now stored on the sales document and is counted as having been used.
Attempting to use that same code again in a sales document will produce an error message, as the code does not pass validation checks. To continue the user would need to use a different code instead.