Great question! First, don’t forget to account for the A string as you move up the neck:
2220 (D), 4442 (E), 5553 (F), 7775 (G)
In the description beneath the tab for that section it states:
Now look at the second chord: G Major. Again we can see that the third string has been removed and we are playing it as an open string. This introduces a C note. If we recall how a major chord is formed, we realize that C is not in G major.
G major: G (1) B (3) D (5)
C is the 4th of the chord. Since C is neither the 1st, 3rd, or 5th of the chord, it is considered an extension. Extensions add color to the chord and will be discussed in an upcoming unit.
So, this chord is really an: Gadd11 but it was formed from the D shape:
7775 but subbed out the duplicate G (3rd string, fret 7 for a C note – open) and the duplicate B note (4th string, fret 7 for a G note – open).
This yielded us Gadd11: 0075
Notes: G (1) C (11) B (3) D (5)
Extensions are discussed in this lesson (further along) in the course.
Hope that helps, let me know if you have any questions 🙂