Vanilla installation instructions can be found here. Note that setting permissions/chowning the directory turns out to be critical, ref here. The web app for managing the server is at localhost:32400. On Ubuntu, the data directory can be found at /var/lib/plexmediaserver/Library/Application Support/Plex Media Server/.
For troubleshooting if the service is actually running, see here. If the directory does not have the right permissions (or runs out of space), the service will not run/break.
Information about moving the data directory can be found here.