The next open tuning you will learn is open D tuning. Open D tuning requires four strings to be tuned down from standard tuning. The sixth, second and first strings are lowered one tone (two frets). The third string is lowered a semitone (one fret). The open string notes as shown in the following diagram will therefore be, beginning with the sixth string;
These notes form a D major chord. A D major chord consists of the notes D, F# and A.