The following video explains the basic Major Scale Formula and how you can see and play it
easily using a single guitar string. This also allows you to say "I can
play any major scale and diatonic mode in any key." It sounds like a
big deal, and it actually is, but it's easy. It is an
essential understanding that you need.
Yes, you can play any Major
Scale or Mode in the time it takes to watch this 8 minute video. This video doesn't cover modes specifically, but if you learn this
formula, you can play the diatonic modes also.
Harmonizing Major Scales in 3rds (below)