This may be a bit of off topic.
But after I couldn't start mocp because of conflict between Pulseaudio and Firejail I became curious about how audio system in Linux works.
I thought MOC connects to ALSA (or JACK...) but apparently it's something to do with Pulseaudio. That's first thing.
Another one is where I could find info in plain English how it all works with audio all the way from audio file to speaker?