Six strings to a string of CGDGAD,
The standard tuning is EADGBE.
Simply put, it is to hold the six-string four-fret by hand or clamp it with a tone sandhi clip, and tune it into the six-string standard tone, the five-string two-fret five-fret standard tone, and the three-fret four-fret need not be tuned, and one or two frets are also two frets.