If you understand your basic open chords, you are well on your way learning the neck of the guitar (even if you don't realize it). If you have learned some basic songs, then at this point you obviously know the five basic triad(*1) chords of C, A, G, E, and D (Hence the acronym CAGED).
Now, I will go into further detail later, but as an example, let's take the form of the basic triad chord C.
Play the C chord slowly.
The first note on the A string is the C note or 1st (root).
The second on the D string is the E note or 3rd.
The third note on the G string is the G note or 5th.
The fourth on the B string is the C note (again!) or 1st (root again).
The fifth on the E string is the E note (again) or 3rd (again).
Now, looking up, just focus on the numbers on the end of those five sentences. There is a pattern developing. Keep going, it will soon make sense.
In a triad chord, the basic rule for a MAJOR chord is that it must have a 1, a 3, and a 5.
1,3,5. The C chord technically only has 3 notes to complete it. There are two roots, and two thirds, 1 fifth.
Once you know where the root fits on this basic C chord, you can then move up the neck of the guitar to create the next note, D:
The last note (the second 3rd) is optional. Most simply play the 1 - 3 - 5 -1 without the third. Practice this in D and other notes up in down the scale. Pick one note at a time, and sing the number of that note for the chord (1), then the second (3), so and so forth. Once you remember the number pattern of C in the CAGED method, you will be able to add scales easily.
