The Kettlebell Swing or Dumbbell Swing is a perfect exercise for developing core strength, power, and some cardiovascular endurance.  The focus should be on the hips.  This is where your power comes from, NOT the arms.  As always, weight stays in the heels, back is tight, keeping the thoracic curvature in place without rounding, and chest stays up with little bending in the hips.  Here are some videos demonstrating good/bad form.