Sorry to hear about that! The new menu works a little different than before, and we'll definitely take your feedback to heart and start thinking of ways to make the first-time experience more intuitive and informative.
To interact with the menu, hold the mallet in your right hand near (or above) what you'd like to select, and pull the trigger button to select. This should let you choose different instruments and access other parts of the menu using the tabs on the left side.
You're completely on point about the importance of the onboarding experience; There are lots of ideas in the backlog about how to make this better, including some kind of tutorial. A lot of the time and effort this year has gone toward rebuilding the app's code from the ground up to be up-to-date with the latest game engine and VR SDK standards, and to support running natively (and performing well) on the Oculus Quest. With that hard work finally behind us, usability improvements and new features are up next!