From the practical standpoint, you have a linux process running from a data directory. You run it, and the you can access it via CLI and via web interface (which also has a terminal-like webapp). It then uses regular IP to talk to other urbits in P2P fashion.
From what I could find, the whole thing is full of magic and pretty opaque - you are only supposed to interact with it by running it and typing commands there. In particular, you’d probably want to back it up. The only instructions I could find is to stop it and tar it up, and back up manually. Better do it often if you want your “digital life” to be safe.