The row is an upper body exercise that builds strength in the upper back, mid back, and arms. The lower back and hips help stabilize the movement.
In the following video, take note of the two main segments of the exercise: Stance, Pull.
Most variations of barbell row do not involve the stabilizing muscles in the hips or lower back, putting most of the strain on the upper back. If you have a weak or injured lower back, these are still effective at building strength in the upper back.
This isolates the movement to one side of the body at the time. The back position and arm movement is identical. Only the stance changes.
This is done seated either at a machine or cable. The back should remain upright the entire time, and the pulling should be done solely with the arms and upper back.