Instead of the user supplying a filename/path for new content, they submit arbitrary metadata. When retrieving content, they query via a language called LQL (Library Query Language).
Basically the system works a lot like ID3 tags for mp3 files. 'Arbitrary metadata' is a lot like the fields for 'title', 'date', 'album', etc except they are arbitrary (you can use any set of key/value for metadata items)
Libraries can connect to other libraries. A 'Library' is much like an email inbox, except its one user per machine instead of multiple users per machine. Each library is 'addressed' via a domain name. All communication between libraries is done through HTTPS.
Traditional filesystems use a permission system that is very archaic. In 1960 it was common for there to be multiple users on one machine, but in 2014, everyone has their own machine. File permissions are useless, since I'm th one person who ever uses this computer. "Permissions" in the 2014 sense is which of my facebook friends gets to see these photos.