upper body to the right, then all the way to the left and back to center for one rep. Repeat up to 15 times per set. Gradually progress until you can complete three sets.
For side bends, hold the weight in your right hand. Place your left hand behind your head or on your waist for better balance. Keeping your hips, back and head aligned, slowly lean to the right. Hold for two counts and return to start. Repeat up to 15 times, switch sides and repeat on the left side. Alternate to the right and to the left to complete up to three sets of 15 on each side.
More information
The American Council on Exercise has more on these and other standing ab exercises and how to do them safely.