The foot files are actually really easy to use and you simply file the callused skin with it. Obviously, you need to take care not to overdo it and do it slowly. It can get warm or hot if you do it too fast or vigorously. Always stop before you get too close to the good skin and always err on the side of caution. If you have diabetes or another problem that puts you at risk, you probably should talk to a podiatrist before using products like this.
After use, brush it clean and depending on the actual product and manufacturers instructions you may be able to wash it under water. It is important that you do share products like this with other people for hygiene reasons. It is too easy to pass bugs on to other people using products like these foot filers.