An artificial harmonic is when you pick a note, and at the same time barely touch the string with the edge of your thumb or index finger. I think the thumb is the most common way to do this, but a lot of people use their index. But the first thing you need to do is crank up the distortion, the gain, and the volume. And by the way, for the best effect, you should pick the note directly above the pickup nearest the neck of your guitar. When you do it right, you should get a squealing, glass-breaking sound a few octaves above the regular fretted note.

-Christoph