Let me preface, I'm nowhere near performing anywhere. C Major is kicking my butt currently. I'm so new that I smell like baby powder.

At my best, I want to eventually be good enough to play and sing with the family. Maybe attend a local jam session.

But, that doesn't stop me from obsessing over what's involved so I can understand better.

Suppose in 2028 I go to a bluegrass jam session. I sit in a chair, take out my tuned guitar, and get ready.  Someone starts "Blue Moon of Kentucky." Then what? Do I need to know how to play the song solo to join in? And how do I know what key? And I guess I'll need to know the progressions (I've not got that far in training, but I know a bit about progressions).