External Storage - general questions

Hello its about the latest OC hosted on a Nas4Free server.

I want to access folders/files on this server via OC. This works via mounting via external storage.

What does this mean? Does OC only mount or does it download files to its own storage folder? Or does it only index the files&folders of external storage into its DB so a user can search on the the external storarager via OC?

I could manage to mount via FTP and “local” folders on the Nas4Free server. SMB/CIFS does not work for unknown reasons. I found some info on the net but if was years old.
FTP gets access to all files in the root / that OC sees.
“local” does not see all folders for unknown reasons?! I have set as global credentials username and pw of a “root” user of the Nas4Free. I assumed that OC would then see all fodlers/files? I think I need help to set this up best (username/pw with proper rights in Linux?).

Can someone explain this to me please?

/local mount is using the ownCloud application credentials and sees everything the www user can see.

There is no coyping of files, it is a true mount. One thing to consider, versioning and trashbin is always using primary storage. This is currently under consideration.