It is not essential to learn to play in all of the twelve diverse keys (twenty-four if you count relative minor keys). The majority of songs with a guitar are written in just a few keys. The most admired keys are A, C, D, E, and G. These keys cover up the octave well, and so it is probable to choose one or more of them for which you will, with your vocal range, be able to sing a particular song at ease. There are more than a few reasons why these keys are popular.

Primarily, they cover the octave well (i.e., wholly and at a practical resolution), so there is no necessitate for more chords (to match anyone’s vocal range). Second, for the guitar they include a large number of “full” and simply fingered and easily strummed chords. By the word “full” I mean a chord that includes all six guitar strings. “Easily fingered” means that typically just 3 fingers are required (in “home” position), and that the fingering is not awkward. “Easily strummed” means that (since the E and A (bass) strings are incorporated) the “alternate bass” strum pattern can be used with no fear of unintentionally hitting a note that is not in the chord.

Lastly, learning chords needs some effort, and there is no point to learning a huge number of them when a smaller quantity will do just as well. From time to time you will have to discover another chord to do a particular song, and you can learn such chords when the need arises.

The “essential” (harmonically related) chords for the keys listed above are as follows:

Key of A: Chords A D E
Key of C: Chords C F G
Key of D: Chords D G A
Key of E: Chords E A B
Key of G: Chords G C D

The preceding keys matching the segment C G D A E of the circle of fifths. These keys include zero, one, two, three and four sharps. Traditionally, music for instruments that are played on the treble clef (e.g., guitar, trumpet, and clarinet) is typically written in keys having sharps, and music for instruments that are played on the bass clef (e.g., trombone, baritone) is frequently written in keys having flats. The limitation of the keys to the set C G D A E is conventional for the guitar.

The fundamental chords for the keys C G D A E match to the full “natural-name” (unflatted and unsharped names) segment F C G D A E B of the circle.

You ought to study all of the “natural-name” chords, A B C D E F G, since these are the vital chords of the five well-liked keys that span the octave (C G D A E). These are “major” chords. As well, you should study all the “minor” natural-name chords, Am Bm Cm Dm Em Fm Gm, and all of the “seventh” chords, A7 B7 C7 D7 E7 F7 G7. Every other chord that you’ll ever require you can learn as you go along.

Learn these chords well, so that you can play them without difficulty by heart, and with no looking at your fingers. When you start, your fingers will get sore, even with nylon strings. In a pair of weeks, your fingertips will build up calluses, and no longer be sore.

There are numerous other chords than the ones (major, minor, and seventh chords) mentioned before, and they are used in a lot of pieces. As you go on, you may desire to learn and use them. They add diversity and richness to music, but you can go with a large number (and proportion) of popular songs without them. To get well on the road to playing by ear, the ones listed above will do just fine for starters.