I read the page “Vocal Reduction and Isolation”, and watched tutorials for removing vocals from songs, and I can’t remove them from a song to make it instrumental.
Try some different songs…
Sometimes it works “perfectly” and sometimes it doesn’t. With most songs it will remove most of the vocals, often with some remaining vocal reverb.
You can’t un-mix audio but it uses an “old trick” of subtracting left from right to remove “centered” vocals as well as everything else in the center. If the vocals are identical (and in phase) in the left & right channels they will be completely removed.
Even when it works perfectly other centered-sounds are also lost so you rarely get a “professional sounding” result. I consider it more of a gimmick.
It doesn’t work at all with mono recordings.
There are a few rare recordings with the vocals on the left or right and in that case you can kill the side with the vocals and make a mono file which will play out of both speakers.
Sometimes it is impossible to remove vocals with Audacity, then other software is needed.