This guitar lesson is a great example of using chord inversions and shapes derived from the CAGED guitar system, and played in the style of “Stairway to Heaven” by Led Zeppelin.
Probably the most recognizable acoustic guitar bit known, the chords of the opening four measures of “Stairway to Heaven” can be notated as: Am-E+5/G#-C/G-D/F#-Fmaj7-G/B-Am. See the guitar tab below as an example.
Alternately, we also see the second chord written as G#+ add B, and other related notations. Slash chords and other complicated looking chord symbols are good indicators that a melodic line in either the bass or an upper voice is important to the progression. This is the case in this song.
In the opening to “Stairway to Heaven” we hear a series of arpeggiated chords accompanying a descending bass line on the fourth string, A-G#-F#-F. This descending bass line supports a melodic line on string one that at first moves in contrary motion to it: A-B-C, then down to F#-E, before the phrase ending.
Which way we choose to name the second chord in the progression, then, is ultimately not that important. As we mentioned, complicated chord symbols are usually a compromise attempting to show melodic lines to the player. In the opening three chords of “Stairway to Heaven,” it is the descending chromatic line in the bass A-G#-G against the ascending melodic line on the first string A-B-C that really creates the character of the opening to this classic song.
Augmented chords and voice leading are taught in the Fretboard Theory video series.