I've been trying to grasp this concept, but like everything else on Guitar, it is very hard. As a warm up, I play the individual notes on the Low E string, than go two strings up and over to hear it again in my effort to begin to recognize them. I've tried to do it vocally, but honestly, the sounds I'm making to my ears all seem pretty much the same. I can differentiate between Major and Minor Chords, but my abilities seem to begin and end there. I've used the Earpeggio App. I've watched Nate and Chelsea's videos on the subject, and yes, they've expressed clearly how difficult this is, how you have to start somewhere. But I'm having a tough time clearing any hurdle on this subject.
The reason I call it the Last Frontier is we all share the basic goal here of making music, to play the songs we like. To have the ability to hear a song, and then actually play it just by listening, no Tab, no Chord Chart?? Sounds like a dream too good to be true.