The kettle bell swing is a hip movement. Its general purpose is to work the glutes and hamstrings. It can start a few different ways; I will outline the one I use the most, here, as I find it to be the most comfortable way to get started.
It should start with the kettle bell on the floor between your feet. Your legs should be slightly bent. Bend over, keeping your back straight, and grip the kettle bell.
Keep your eyes focused on the kettle bell.
Contracting your glutes and leaving your arms straight, stand with the kettle bell. This should look like a deadlift.
You should now be standing with the kettle bell between your legs, in front of, but touching your body.
Your shoulders should be rolled back and not slouched forward.
Keep your legs slightly bent, and begin to sit your hips back, just a bit. Thrust your hips forward, pushing the kettle bell into the swing motion. This may take a few swings to get the motion down, and you may find yourself using your pelvis to physically push the kettle bell forward; that is ok.