The target: Your thighs, hips, and abs
Grab a dumbbell with both hands and hold it by its ends next to your chest. Stand tall with your feet hip-width apart [A]. Step forward with your right leg, and lower your body until your front knee is bent at least 90 degrees and your rear knee nearly touches the floor. As you lower your body into the lunge, rotate your torso toward the same side as the leg you're using to step forward [B]. (For example, if you step forward with your right leg, rotate to your right.) Reverse the movement to return to the starting position, then repeat by lunging forward with your right leg. Alternate back and forth.
If that's too hard: Perform the exercise the same way, but without using a weight.