A thumbwheel switch is a multi-position rotary switch. It contains a sprocket that can go forward or backward. As you can imagine from the name, you will be able to use a thumb, or a finger, to move the sprocket each way. They can be on a mechanical or an electronic device. These are sometimes called digital switches, and you can see them in action on a variety of different devices. Some of them are very simple, while others are going to be quite a bit more complex.
You can find some models that have push pen operation so that you do not trigger them accidentally. Others have locking mechanisms for the same reason. Many of the items on the market are going to be quite simple to use, and they will have large numerals so that it is easy to see them. The larger numerals help to eliminate the chance of there being an error on the part of a human.