As you see, you can connect any directory in the document management system to an Open ERP resource. The system then manages its creation and keeps the directory synchronized with the reports generated by OpenERP from its own data. You don't have to create or rename these directories because OpenERP does all this automatically as it resychronizes with its own database.
You can then copy the files in the directories that correspond to any of the resources. The files are automatically attached to OpenERP's documents through attachment management. Conversely, if you attach a document to one of OpenERP's resources then that document will automatically become visible over FTP in the document management system.
If you don't install the document management system then the files that are attached to an Open ERP resource are stored directly in the database. Once the document management system has been installed, the contents of the files are no longer stored in the database but are stored instead on the Open ERP server filesystem in a directory named 'filestore'.
You can then read and add attachments to OpenERP resources quite independently of the OpenERP interface or the FTP server using simple drag and drop.