These bell like tones are created by placing your finger very lightly on certain areas of the strings while plucking.
These areas are called nodes and playing them causes the string to vibrate in equal divisions resulting in higher pitched tones.
The easiest natural harmonics to play are at the 12th, 7th, and 5th frets. For best results press lightly and pick near the bridge.
The graphics below show which notes are created by the natural harmonics on the guitar neck.
The graphic shows which notes are created by the natural harmonics on the guitar neck, and how each node effects the string when played.