The Key of A — Guitar

A major harmonises to A – Bm – C#m – D – E – F#m – G#°; A minor to Am – B° – C – Dm – Em – F – G. Most of the country repertoire in this key lives on three of those chords — the tonic, the subdominant and the dominant — plus the relative minor when a song wants one darker turn.

The guitar chair carries the boom-chick floor — a bass note on the strong beats, a strum answering it on the weak ones: the shape below is what a right hand strums, and which bass note opens it decides how the boom half of boom-chick actually walks.

Learn the tonic-subdominant-dominant grammar in A until your hand goes there without asking, then add the relative minor, and most of the repertoire in this key is already playable.