How do I record while simultaneously listening to another track or instrumental thru the headphones? instead of thru the loud speaker or monitors?
I’m using a scarlet solo gen 3
I think you are looking for Tutorial - Multi-track Overdubbing. See here: https://manual.audacityteam.org/man/tutorial_multi_track_overdubbing.html
I hope this helps. 
listening to another track or instrumental thru the headphones?
Fair warning that even though it doesn’t explicitly say so in the tutorial, you can’t do “perfect” overdubbing with wireless headphones.
You can absolutely do overdubbing, play along with an existing backing track and record yourself, but you can only hear yourself mixed in real time by listening to the device or microphone, not the computer. And you can only do that with wired headphones.
Koz
Another fair warning. Overdubbing has to play the backing track to you perfectly and record you perfectly, at the exact same time. This is where we find out if your computer is up to it.
It’s also a terrific idea to close everything else running and restart the computer before the performance. There is no leaving Zoom or a game running in the background while you’re overdubbing.
Koz
Sorry guys, this is the only way I can find to make any contact with this forum! How on EARTH do you start a new topic? There’s no way ‘in’ that I can find! Where’s this fabled ‘New Topic’ button; nowhere that I can see, after 20 minutes of faffing!
As you are on Windows:
- Go to the Windows forum: https://forum.audacityteam.org/viewforum.php?f=46
- Click on the “New Topic” button (on the left, just below the “forum rules”)
I hope this helps.