Watch the Harmonics online guitar lesson by Dmitry Lisenko from Percussive Acoustic Bass (Foundry)
Harmonics are amplified overtone notes, they have very high pitch, and that's why they sounds amazing together with low bass register notes. Lightly touch the strings (don't press down) directly over the fret wire and pull the string. Keep in mind that you have to be very precise on fretboard and apply the correct amount of pressure with your right hand. You can also play two or more harmonics together creating intervals in chords. Experiment and try to find your own combinations.