Cupping like gua-sha dates back thousands of years.  It has many
forms. The cupping in modern day Chinese medicine usually comes 

in the form of glass or plastic cups. Fire is the original way the oxygen is
taken out of the cup to provide suction.  The plastic uses an air
pump.The suction of the cup lifts the tissue allowing better blood,
lymph and what we call qi  (life force) to flow. When used as a
sliding cup it provides myofascial release. This can facilitate
obstructions that stagnate in the body. It can treat nueromuscular
pain, repetiive joint and trauma injuries. You may have seen this
where it especially popular in sports.

Cupping can also help move toxins in the body that might be
circulating in the tissues, such as from colds, the flu or lymph
congestion. It can also be used for digestive disorders facilitating
intestinal peristalsis and fluid movement.  Discoloring, if used
correctly can be diagnostic to areas of obstruction (purple) or to
much heat in the body (red). Very pale or no color is deficient blood
supply. It shouldn’t be discomforting so inform your practitioner with
feedback when receiving this treatment.