It involved the tongue your lips, and being able to use your voice box to generate noises if you want to emulate instruments or bass tones. Dana Carvey is awesome as impersonations, if I spent 8 hours a day for the next 10 years practicing I still couldn't sound half as good as him. Anyone can basically beat box, but to sound good doing it isn't easy. Beardyman is gifted, sort of like Jordan, working on their talent will increase it but the natural ability they have won't be touched.
I spent the better part of my later childhood trying to learn how to Beatbox, and I still sucked at it. Ended up giving up on my dreams when I was about 12. hehe. Hell I can't even seem to get that good ar Counter Strike, I guess I'm just epic fail.