Try a search on the forum - there have been a few threads on this over time.

Briefly:

natural harmonics are created by touching the string above the fret wire and picking the string (try 12th fret for an idea). you'll get a different note from fretting over different frets - try 5, 7, 12 & 17. Don't hold the string to the fret though, just rest your finger over it.

Artifical harmonics (AKA Pinch Harmonics) are acheived by hitting the string with your thumb right after the pick hits the string - it's harder than getting natural harmonics, but once you get the technique, no problems.... you move your picking hand to get different notes...

try the forum search man.... we've talked about it loads.... :D