The Key of D — Guitar

D major harmonises to D – Em – F#m – G – A – Bm – C#°; D minor to Dm – E° – F – Gm – Am – A# – C. 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 D until your hand goes there without asking, then add the relative minor, and most of the repertoire in this key is already playable.