There is a right and wrong way to row however, as I found out from a personal trainer at my local gym.
Rowing works all the major muscle groups in the legs, arms, back, abdominals and chest and gets the heart rate up.
The explosive press of the feet helps to build strength for pushing off the wall. The pull by the arms for building up the lats, chest and biceps for the arm stroke.
Rowing is a pushing activity, not pulling as you might think. At the start of the 'catch' phase (crouched close in to the wheel) the power comes from low down in the body, the large muscles in the legs. Its not until you push back and the legs are nearly straight that the arms get involved. By the last part of the active push you should be just past upright, keep your back straight and core engaged.
During the recovery phase let the hands move back with the handle first, don't bend your knees until the hands are at shin position, as you then return to the starting crouch position. This is the mistake many people make, they push out and in with the legs.
Steady rowing can give an aerobic workout, whereas interval rowing with high intensity bursts, interspersed with easy rest periods, can give an anaerobic workout.