Moxibustion therapy is an ancient form of heat therapy using the leaves of the Mugwort plant. The Chinese would take the aged Mugwort plant and grind it up until all that was left, structurally, was a fluff of leaf fibers. Those leaf fibers are then either rolled into a stick for indirect moxa or shaped into a cone for direct moxa.
Some even make moxa spheres to apply to the handle end of a needle. This method is used to warm needles that are in the body. The burning ball of moxa on the needle conducts heat down to the muscle layer and is good for muscle or joint pains.
The Mugwort herb itself has an indication of "promoting circulation" or "stimulating blood flow." This is why often times acupuncturist will also use it for menstrual issues as well (ie. painful periods).
What's that smell??
Burning moxa has a distinct odor of, well, a burning herb. Some people at my Loveland Acupuncture practice find the fragrance to be soothing and relaxing. Therefore its application also serves as a type of aromatherapy.