The idea behind this device is that you put fit the lid into the opener into the hole where it fits tightly. You don't go with the hole that is too big because you need the opener to be able to squeeze tightly on the lid. There are four different sized holes. If your container looks like it could just barely fit in a hole, you can spread the handles in order to make it fit which will actually help with opener in. Once the lid is fit in the device, you squeeze the handles together where it is it most comfortable for your hand, twist, and open the container. There are grooves in the handle to make it more comfortable for your hand and fingers. It is also coated in food grade polypropylene and rubber to make it non-slip.
I got this with my mom in mind. For people who have arthritis, doing something as simple as opening a jar can be nearly impossible. She has arthritis really bad in her hands and can barely open jars and bottles. This will give her the leverage she needs and a wide enough grip that she will actually be able to open things again. I will be giving her something that most of us take for granted. She hasn't had a chance to try it out, but I tried it out on four different containers. I really don't understand what cans you would use it on because the different between a can and a jar to me is that a jar has a lid and cans do not. Somehow it can be used on cans though.