The "wonder how to" article is wrong in multiple ways:
1) "Removing vocals from any song is a super-easy process"
No it isn't. Removing vocals from "some" songs is super-easy, but for "most" songs it is difficult or impossible.
2) "Split the Track"
In very old versions of Audacity this would have been correct, but in more recent versions you should "Split Stereo to Mono".
3) "You may notice you can still barely hear the vocals. If that's the case, go to Effect -> Amplify and choose a negative level value—you'll want to play around with the exact values until you find one that works best for your specific track."
This is just wishful thinking. "Theoretically" tweaking track levels could provide some improvement in a very few, very specific cases, but in the vast majority of cases it will make the separation worse.
4) The entire process is obsolete because Audacity has shipped a "Vocal Remover
" effect for many years, which automates this technique (correctly) in a single click. Note that this effect is now classed as "legacy" (because it has been superseded by a better version) and will be removed at some future date.
5) The tutorial never once refers to the manual, which is kept up to date with all the latest features.
For current information about vocal removal / vocal reduction / vocal isolation, see here in the manual: http://manual.audacityteam.org/man/tuto ... ation.html