The one-arm row is a weight training exercise that targets the muscles of the back, including the lats, traps, and rhomboids. It is typically performed using a single dumbbell and a flat bench or other stable surface. 

To perform the exercise, you will need to stand to one side of the bench and place your opposite knee and hand on the bench for support. From there, you will need to grip the dumbbell with the hand on the same side as the supporting leg and lift it up toward your chest, squeezing your shoulder blade together as you do so. Be sure to keep your elbow close to your body and avoid swinging the dumbbell or using momentum to lift the weight. It's also important to use a weight that is challenging but manageable and to avoid rounding your back or arching your lower back during the exercise. 

Once you have completed the desired number of repetitions on one side, switch sides and repeat the exercise with the other arm.