Stair climbers are excellent machines for cardiovascular conditioning. They are not meant for strength training and will not give you big muscles.
The major muscle group used is the quadriceps. Stand upright on the machine and use the hand rails only for balance. If you support your weight on your arms and take tiny steps, you can light up the display but will not be getting the aerobic workout you need. Use a lower level if necessary and do the work with your legs, taking a 6-8 inch step, keeping your foot flat on the pedals. This will burn calories, improve cardiovascular function, and strengthen your bones.