How to install Minecraft Velocity proxy?

Velocity allows players to switch to multiple Java servers from a single address. Proxy and backend servers use separate processes and ports.

Step by step

Start Velocity jar in a separate folder and open the created velocity.toml file. Set the listening address available to the player.
Define the real addresses and ports of the lobby and other backend servers in the servers section. Add the target to the list during first login.
Match modern forwarding setup on paper backend servers. Limit network access so players can't bypass the proxy to backend servers.
Enter the proxy from the external network and switch between the lobby and the other target. The direct back server address should not accept external connections.

Announce Velocity's port open to the player as the player address, not the port of the back server.