How to Tune a Guitar to Itself Using the Fifth-Fret Method
Play the fifth fret of the low E (6th) string and then play the open A (5th) string.
Let both notes ring together. Their pitches should match exactly. If they don't, determine whether the 5th string is higher or lower. If the 5th string seems lower, or flat, turn its tuning key clockwise to raise the pitch. If the 5th string seems sharp, or higher sounding, use its tuning key to lower the pitch.
If you can’t tell whether the open string is higher or lower than the fretted string, tune it flat intentionally (that is, tune it too low) and then come back to the desired pitch.