What is Open D Tuning?
Open D tuning is done when all strings of the guitar are tuned in the D-A-D-F♯-A-d pattern. So when the strings are strummed without holding any notes on the fretboard, they give out a D major chord. Similarly, if you barr the second fret throughout and strum, this would give you an E major chord. Barring the third fret will give you the F major chord,