Hello Eric,
The CODM user's guide is on the Help menu in Hauptwerk and should cover everything you need to know, as well as how to get started As covered in it, there are also various example CODM organ definition files installed into [Hauptwerk installation folder]\HauptwerkUserData\CustomOrganDefinitions.
Start by going through the guide and looking at those examples, then make copies of the files and experiment with editing them.