It's late and I can't sleep (should not have taken that nap today) so you will get an answer about "how we learned it"...or better yet "how and why I learned it".
I was the typical guy that made most of my chords within the 1st 3 frets...you know those chords that we all learn to make when starting out. Well I seen this entire part of the fretboard not being used (well wait, I could make the "power chords" like rockers of the time did also). I seen other guys understanding the entire fretboard...what were those foreign chords? Why do my leads when I would attempt them sound like crap? What is the secret that these guys know and I don't?
Me, I am a "If Joe Blow can do it then I can also" type of guy - determined and bull headed. So I put it in my head that I was gonna learn music theory. Now it was a rocky start but the only way my head could approach it was from a "mathematical perspective...I do love math! So I dabbled into the "math" behind the music and learned a lot of things about music - but math can't teach you to play!
Then I got into "theory" of scales. I had already dabbled into the minor pentatonic scale but really didn't understand why it was what it was so I researched more. Found out that probably 95% of "rockers and blues guys" relied only on those 5 notes to play lead with...damn I am really feeling stupid now as it's only 5 notes adn I can't do it like them....must be the under-developed "artist" in me!
So I just dive into Youtube videos. Learning Theory is just like learning to flat pick, it takes hours and hours of time to grasp then one day it just kind of "clicks". Clicks in a sense that you can within about 2-3 seconds identify any note on the fretboard, see "chord shapes" when you look at the guitar. See scales (The major scale around a chord, the minor pentatonic around a chord, and the "blues scale" around a chord...they kind of just pop out at you after a lot of repetition...pop out in the same sense that you should be able to look at your guitar and visually see how to make a G chord...di you learn that over-night - No, it came from repetition try it, set your guitar in the corner and tell yourself to look at it across the room and fret the strings "in your head" that make our ol' standard G chord...yep if you can see it then you can visually memorize about any pattern on the guitar - scales are "patterns" chords are "patterns" and it will start opening up the rest of the guitar for you!
Understand that there are only 12 notes on a guitar and that our pee-brains make it harder than it is to learn it! The "major" scale is probably the toughest to learn and it only consists of 7 of the 12 notes.
When one dumbs it down to that level and sees that it's not that intimidating then the learning process can start.
Youtube videos are your friend when it comes to theory. I learned all of my music theory through Youtube and some reading "here and there" on the internet. Now since we have the "theory" here I feel I can learn what I don't know from folks on here. For the record I have had one music lesson in my life and that was with Ben and I wanted to understand improv a bit better- basically we sat on his couch for 4 hrs and "told stories" not even music related and worked in some ideas between the bs'n. I can "teach" myself anything and youtube videos are so much more efficient then reading!
Where I am at now: I have a solid foundation on theory, a solid foundation on flat picking, a solid foundation on music in general...I tend to fall apart on improv! I can only keep it going for a few measures then it kind of falls flat on its face. So now I am all wrapped up in "ear training" in order to help me hear what notes I want to go to next or what phrase I want to make. But just like "theory" and on day one when you decide to start learning to "make a chord and strum" the guitar...it all takes baby steps.
Determination is why I learned everything I have about music - and don't think for one moment that I was a "natural" - hell no! I have fought it every step of the way!
I have done what a lot of folks think are "pretty impressive things" in my life. Was in the 1st gulf War, have a nuke background, managed to go from a high-80's golfer to a scratch golfer in 1 year and got a college scholarship -even won a college tourny! Started a business from ground up at 29 years of age - Delivered my 3rd kid on the bathroom floor - and was retired at 42 (until last week when I accepted a VP position).....but anyway what i am getting at is that "music" and learning to play an instrument and all the technique and theory that goes with it is the most difficult undertaking that I have ever attempted in my life - hell I even got my engineering degree in just over 3 years by taking 20+ credit hours each quarter in order to get it over with and even the calc, physics, chem classes didn't kick my butt as bad as music did when I decided to "really start" learning it.