Watch the Natural Harmonics online guitar lesson by Jeff Scheetz from Rock Tricks
Natural harmonics occur "naturally" at certain places on your neck. It has to do with string divisions and is a logical mathematic problem. But since we wanna "rock" - we are not going to get bogged down with something pesky like math.
Suffice it to say that you can hear natural harmonics from many bands, both electric and acoustic, and adding them to your arsenal will make you a more complete player.