You made it up to here, you finished Part 4 - Setting up Rclone and/or Plexdrive and are still with it, congratulations! The hardest parts are done, it'll be downhill from now on. Promise!
Finished Part 2 - Configuring Ubuntu ? Then you can proceed with the installation of Plex itself. Thanks to an awesome script that is available for free, this is going to be a breeze.
So you're thinking of starting a media server on a VPS with infinite storage on a cloud service, but you have no idea where to start. This sounds like me, a few weeks ago - I found the installation absolutely daunting!