Why does the localhost server not work?

[Hashimk2]

when you click the servers on suroi.io, the top one is localhost server, but when i click it and play solo, squads or duos, it says, 'error joining game'

[kidwaih2]

There was a mistake, the localhost server is not supposed to be there. Just play in any other servers (you can close this now)

[Crimson-Haze]

What does it do?