First run
Create your account number, answer three questions, and see the first lyric.
Two screens stand between opening 9xLyrics and reading a lyric. Neither takes long, and the first one matters more than it looks.
1. Your account number

Create my free UID mints a twelve-digit number and starts a 3-day trial with everything unlocked. Use an existing UID signs this machine into an account you already have — including one from another 123sudo app.
The number is then shown once, and the app waits.

Save as .txt writes it to a file with a line explaining what it is. Do that, and put the file somewhere that is not only this computer. There is no password reset, because there is no password — see Your UID and devices.
2. Three questions

- What would you like to see? — pick a surface. Floating Lyrics is the default and the one most people keep. A free account runs one at a time; during the trial you can turn on all four and see which you actually use.
- How should it look? — theme, and the background behind the words.
- Where is your music? — which player to follow, or Automatic, which follows whatever is playing now.
Skip setup goes straight to Settings with the defaults. The guide is not gone: Settings › General › Setup guide › Show again brings it back.
3. Play something
That is the whole setup. Start a song in Spotify, Apple Music, a browser tab or anything else your system knows about, and the words should appear within a few seconds.
If they do not, it is almost always one of two things — the player is not being detected, or that song has no synced lyrics anywhere. Troubleshooting starts with both.
Where the app lives
In the tray, or the menu bar on macOS. Closing the Settings window does not quit 9xLyrics — it goes on watching in the background, which is the point of it.

To quit properly, use Quit 9xLyrics in that menu.