um.... i might be wrong here, and if i am i apologize in advance. when you lightly touch the strings its a natural harmonic. artifical harmonics are when to note "squeals" at a higher register. listen to zz-top for examples

to do them you need to catch the string a little with your picking hand as you play the note. unfortunetly its kinda difficult to explain, one of those things that you can't explain, only demonstrate. just trying picking the notes with a little force and some drive, keeping your hand close to the strings. sorry i can't be of any more help