The basic file structure for your module will be divided into two sections, the admin and the catalog folders. The contents of each folder will follow the MVC-L framework respectively, with the difference that the admin will deal solely with backend functionality, and the catalog with frontend functionality. Users of your module will interact and configure its settings in the administration side of the store. Therefore, the files in the admin folder will handle any changes to its settings, the way the module is displayed in the administration, install/uninstalling the module, etc. Likewise, the way the module is displayed and how it works in the front end of the store will be handled by the files in the catalog folder.