Take a big step forward with your right leg. Bend so your knee is straight up from your foot, but not over your toe. Take a wide stance so you're on the ball of your back left foot, which also stretches your left hip flexor. Grab a weight, like a heavy can, with both hands and bring it up by your right ear, then swing it down to your left hip.
Contract your stomach - squeeze it like a fist as you swing the can down across your body, and if possible, bend your knees a little deeper.
This rotation will work on your entire core area of your back and abs, with emphasis on the obliques located on the sides of your core.
You will no doubt notice you will also be working your hips, thighs, and glutes as well, and if you keep the knees bent, you'll also experience a balance challenge.
Chop smooth and even for one minute, and then switch legs and arm direction for the other side.