Currently the system is in test phase. The process is pretty simple:
Go to https://music.3dxchat-status.com
Register an account (no worries, no e-mail verification required)
Get a YouTube URL from a song you want to get played ( youtube.com or youtu.be/watch?v=xxxx)
Queue it and wait until it's your turn
The YouTube song will get played in the Saloon
Your song can be introduced in 3 ways:
You can come up with a custom phrase, it'll get pronounced by an A.I. voice just before your song starts
You can record a sample with your microphone, it'll get played before your song starts
If you don't do any of the above, the song will be played after an A.I. saying "This song is requested by $nickname"
Right now it's not certain how and if this system will get implemented, @Gizmo picked the Saloon for this test phase.
Good to know
You can queue YouTube videos of 5 minutes tops
You can queue two songs max
Troll songs or non-music videos will get removed from the queue when noticed
You can delete your own queue entries with the little garbage bin icon
Sometimes preparing YouTube video's fails: You can retry, sometimes it works the second time. You'll get a notification when that happens.