How do instrumental musicians make music?

Not really. It’s generally deliberate, confined in a scale or written note for note.

There is a chart or plan, with chord progression and it is known to musicians (written music or charts).

In the movie, “Amadeus” the genius Wolfgang Amadeus Mozart could hear the music in his head and then he just wrote it down on paper. Made other composers feel mediocre.

A lot of ‘rock n roll’ songs use A7, D7 and E7 chords.

Not likely.

Easy Peasy. Just like this
https://youtu.be/inGgpJuJHUc

Seriously though, in my case I hear a tune, get the chord structure of the tune in my head and then go from there. Most bluegrass songs are reasonably simple and follow patterns so as long as it’s in a friendly key I can usually do something with it.

Blues can be in Key of “A” with 7ths, so it is A7 – - D7 – - E7 – - A7 – - -D7 – – A7.

@Caravanfan Is that you playing banjo?

@Blackwater_Park On the video? lol no. I’d be happy if I were a tenth that good. No, that’s Michael Cleveland and the Flamekeepers—a stunningly good bluegrass band.

Noticed the mandolin player could shred that little thing.

@Blackwater_Park https://www.youtube.com/watch?v=TO6tn6g8098