Rowing is a great aerobic exercise. You will find that the range of upper body movement quickly gets your heart and lungs working hard and this will help to increase your stamina over time.
In fact rowing can be so strenuous that you should not be tempted to aim for higher work-rates when you start out. It is not necessary to pull with the most resistance or the fastest split-times for you to get a good workout.
In fact, many rowers will advise you that in order to use your row machine correctly, you should set it at something like 7 out of 10 for resistance, as this will get closest to the work needed for rowing on real water.
Once you have built up your fitness and stamina a bit, you can then move to trying for faster split times and if done correctly, this will help to build up your strength in both your legs and arms.
Try to set a stroke rate of around 30 per minute and gradually bring down your time for a fixed distance. Then see if you can make fewer strokes while keeping the time the same (down to around 23-25 per minute) - this will increase your arm strength. Now, if you switch back to 30 strokes per minute, you should see your time drop even further.
As with all exercise, build up to this and listen to your body and your doctor - especially if you have back problems. This is a great way to start helping those muscles but don't dive straight in at the top!