Music Theory Lesson 3 - Understanding the chords in keys

Great stuff.. thank you.

Is there a chance you can explain how the chord building works on guitar? You have showed how to build a chord from the root note with going up 2 tones in the scale twice. On keyboard it made sense how you showed it.. but on guitar i dont get why on some chords you leave out strings or which string to play which note on.. if you get what i mean. And also i have seen that chords are variable? For example on Ultimate Guitar where you can look up TABs for songs, some of the chords are played sligthly different sometimes, like the G chord where sometimes you play the B string without fretting and sometimes you play it on 3rd fret.. how come so?

2nd !

Cobra Kai never dies!!!

Metallica