Screw the air hose onto the threaded valve on the underside of the airbrush.
Attach the other end of the hose to your air source, whether it be an air compressor or CO2 tank. Both typically offer a threaded valve of the appropriate diameter and thread pitch.
Remove the lid from the container of airbrush makeup. Screw the container to the threaded socket on the underside of the airbrush.
Power on your air compressor or open the valve of your CO2 tank to commence airflow.
Practice using your airbrush on a large sheet of paper. Pressing down the trigger on top of the airbrush releases the air stream. Pulling back the trigger will dispense the paint. The farther back you pull the trigger, the more paint is released.
Wash your legs thoroughly using body soap. Rinse your legs and pat them dry with a clean towel.
Sit on a chair and place a stool in front of it. To protect your work area, cover the floor, chair and stool with newspapers.
Prop one leg up on the stool and begin applying makeup paint with your airbrush using long, up-and-down passes. Pull the trigger all the way back when shading to make a thick, opaque layer of paint. For a lighter layer, press the trigger back gently. Repeat until your leg is completely covered or the desired effect is reached.
Repeat the above step for the other leg. Allow both legs to dry undisturbed for the time suggested on the makeup container.
Wash the makeup off during a shower. Use a bristled scrub brush and body soap to remove thick layers of makeup.