The Arnold press is used to work the shoulder muscles through a full range of motion so that you hit more muscle fibers with one movement.
Begin by cleaning 2 kettlebells up to your shoulders and then place your legs at approximately shoulder width apart. Make sure that your palms are facing your body, but still have the kettlebell resting on your shoulder. Next, press the kettlebell straight up overhead; as you press the kettlebell rotate your wrist so that your palm is facing away from you at the top position. Return the kettlebell to the starting position with your palm facing your body. Repeat this movement until your set is complete.
Make sure to hold you core tight and look straight ahead throughout this movement.
If you do not know how to complete a kettlebell clean see the exercise guide for kettlebell clean.
You can also do this with one arm at a time in an alternating fashion or with completing your set with one arm and then repeat with the next. You can also do this movement seated.