The ear reflects the body, in an inverted fashion, as shown in the following diagram.
A match stick can be used to gently prod the areas to find sensitive areas which may be related to the body parts. Problems may also be reflected as a change of colour of the skin, or superficial capillaries.
A variety of methods may be used to stimulate the points.
Press spheres are widely used. These are small metal balls made of stainless steel. Some are silver or gold coated or may be magnetic.
Map of the ear. Source; Essentials of Chinese Medicine- Beijing.