As you see, you can connect any directory in the document management system to an Odoo ERPOnline resource. The system then manages its creation and keeps the directory synchronized with the reports generated by Odoo ERPOnline from its own data. You do not have to create or rename these directories because Odoo ERPOnline does all this automatically as it resynchronizes 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 Odoo ERPOnline's documents through attachment management. Conversely, if you attach a document to one of Odoo ERPOnline's resources then that document will automatically become visible over FTP in the document management system.
If you do not install the document management system then the files that are attached to an Odoo ERPOnline 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 Odoo ERPOnline server filesystem in a directory named 'filestore'.
You can then read and add attachments to Odoo ERPOnline resources quite independent of the Odoo ERPOnline interface or the FTP server using simple drag and drop.