To perform the exercise, grab a dumbbell, plate weight, medicine ball, or anything semi-heavy and hold it in both hands in front of your torso. To get in the starting position, press your hips back, bend your knees, and squat down slightly (not a full squat), rotating your body to the right until the dumbbell is positioned just to the outside of your right knee.
Keeping your arms straight throughout the exercise, tighten your core and extend your knees and hips to stand up, and as you do, "chop" your arms diagonally up across your body, reaching the dumbbell over your left shoulder. Reverse the movement, and as you return to the semi-squat, "chop" the dumbbell back down and across your body. Make sure you really use your abs to control this cross-body motion to keep your spine neutral throughout.
Aim to perform three sets of eight to 12 reps to each side. If you're new to the exercise, you may want to start without weight, just to master the movement before making it more challenging.