It's a leaderboard of sorts where players can submit their scores.  You need to create a character on the website first (create character in the game basically just loads the Metaverse page here on the site) and then you're good to go.

Metaverse games disallow the use of cheats, and you won't be able to use most mods while playing either.

You can join a metaverse empire and then the scores you submit on that character will count towards the empire's score.  The downside, as I've already mentioned, is the inability to use most mods while playing metaverse games.

If you're just playing DL or DA, you'll probably get a decent challenge from the AI without mods; if you play TotA, not so much in some cases.

Anyway to answer your question more directly, metaverse isn't really a multiplayer option.