It works by tuning the high e (open 1st string) with a normal tuner or with who your playing with, this is your reference point. All the other strings will be tuned by ear to this string.
Play the 12th fret harmonic on the b string then play the same note on the 1st string and tune the 2nd string to the 1st. Playing each note so they ring together is vital. As the note that is being tuned gets closer to the reference pitch you will notice the oscillation slow down until it disappears, they will be then sounding the same note exactly. Repeat the process with the 12th harmonic on the g string to the 3rd fret 1st string g. Next is the d string 12th harmonic with the 3rd fret d on the b string. 12th fret harmonic on the a string to the same a note on the g string. Finally 12 fret harmonic on the 6th string to the 2nd fret e on the d string.
Each String is now tuned to the first open e. The Tuning method shown is for standard (EADGBe) but there no reason why it cant be used on different tunings.
Eric Roche - While my guitar gently weeps (Beatles cover)