The arms is an integral part to piano playing. My instructor places the part right behind the shoulder as the most important location when playing the piano. Piano playing involves not just the fingers. It involves your whole body. Try this. Move your elbow a little bit to the left and a little bit to the right. Then move only you wrist a little bit to the left and a little bit to the right. Which do you think covers more area more quickly? The elbow, of course! And if you keep going up the arm, you'll find movement easier and easier. The first part to being able to use your arms is to be able to relax them, and to relieve them of tension. This will take a while to master. For some, several months, maybe even years, to achieve a perfect relaxation even while playing intense octave passages. This will reduce strain and arm injuries, and you will be able to play more tiring pieces with a better ease. Second part is to be able to know how to "walk" on the keys. Basically, when you stand up, do you exert a lot of power to stay standing and place your feet on the ground? You never go around stomping all the time to stay standing and to walk? You use almost no energy to stand up, and it doesn't hurt to stand up, either. There is no excessive energy wasted, and people would notice that you are heavily straining yourself. (This is an important use for having a teacher. You can never watch your arms while you play. Of course, there are millions of other reasons for having a teacher, but this is a real important one.) So, you have to learn to achieve a similar effect while playing piano. Being able to walk on the keys helps a lot, and makes lots of piano playing a lot simpler. My teacher found Chopin's Op. 10, No. 2, to be less difficult than the other etudes simply because he had known how to use his arms and the other techniques here. He also has a virtually perfect legato on that piece, too. (With no pedal!). There is a lot more to using your arms, but this is just a short, condensed version. I hope this helps.