This is a great feeling machine and is used to develope your Latissimi dorsi (Lats). You use it like you are trying to do a pull-up. Flex your lats down before you start pulling with your arms. You can also use a "reverse grip" which is like a chin up. Try doing a couple of sets using both hand positions for something new in your workout
The latissimus dorsi muscle is one of the largest muscles in the back.