The seated row is an exercise for your entire upper back. It primarily works the lats and the rhomboids. And it will also work the middle and lower traps, the erector spinae in the lower back, and the teres major of the sides of your back. The shoulders and the biceps worked as secondary muscles. The glutes and hamstrings act as stabilizers.
The row is a great exercise to strengthen and build thickness in the back muscles. It can also be done with free weights. The seated cable row some benefits over the free weight version. It is relatively safe and fits better for beginners. Using free weights often require you to be in a bent-over position. This puts a lot of stress on your lower back and it is much more difficult to execute with a good form, especially if you're using a heavy weight. So the cable row might be a better choice for people with back problems.
The seated cable row is quite versatile. You can use different attachments to change the muscle involvement. A wider attachment will involve more of the lats and help you build more width through the back. You can also use a straight bar to hit your muscles differently, an overhand grip will isolate your back more and reduce involvement of the biceps. While the underhand grip involve more biceps, usually allowing you to use more weight.
If you don't have a seated cable row machine, you can do the same exercise on a regular cable pulley. Just set it on the lowest option, and sit on the floor in front of it.
Focus on your back muscles, you should feel this exercise working your lats and back. Don't turn it into a curl, where the movement is done only with your arms. Think of your arm as merely a hook to connect the resistance to your lats and mid-back muscles.
Keep your back straight, chest up and the shoulders pulled back and down. Do not hunch the shoulders forward or round your back, if that happens it is usually an indication you are using too much weight.
Keep your torso still and upright trough the movement. Don't lean back as you pull the weight or lean forward as you let it return. Rocking your torso back and forth will shift the tension off your lats towards the lower back. Remember that just because you can move the weight stack doesn't mean you're working the targeted muscles effectively. Use lower weight if you find it too difficult to keep the torso still.
Move the cable in a slow and controlled manner. It is very easy to use momentum for this exercise, and although it will feel easier, your muscles will work less effectively, and you will be more likely to break your form.
Stop lowering the weight a little before the weights hits the stack. This will keep the pressure on your muscles through the whole set, resulting in bigger muscle growth.