Want to use auto-duck. Need control track-Windows xp

I’m using the latest version of Audacity. Want to do a narration with music mix using autoduck. popup says I need a control track. How do I create/add one. thank you.

http://manual.audacityteam.org/o/man/auto_duck.html
Koz

In Audacity you must have the track you want ducked immediately above the track ducking it.

If you select a track to duck which does not have a track below it you will get that error message …
AutoDuck error message if track selected to be ducked has no track below it.png
So in your case you must have the music track (you want ducked) immediately above the vocal track (a/k/a/ the control track ).
The controls to move tracks up or down are in the drop-down-menu, see … Audacity Manual