Kinda easier to explain in person. Well the string holds the ink and as pressure is put on it some ink is released. The bamboo is in sharpened spikes of varying lengths (depending on purpose and personal preference) and is either twisted (rolled) on the skin to puncture or inserted at a slight angle directly. Each pass only (depending again on the shape of bamboo) usually makes a single dot, so even small tattoos take hundreds of times longer than mechanical ones do. I use india ink, but in tibet they are known to use a mixture of charcoal and snake venom among other things (its a secret). Those tattoos are known as magick yantra tattoos and only monks may do them. I would love one someday