![Tactile Switch Buttons (12mm square, 6mm tall) x 10 pack Tactile Switch Buttons (12mm square, 6mm tall) x 10 pack](https://cdn11.bigcommerce.com/s-2fbyfnm8ev/images/stencil/500x659/products/1877/6712/apitkgugk__23325.1554988213.1280.1280__78114.1666613516.jpg?c=2)
Medium-sized clicky momentary switches are standard input "buttons" on electronic projects. These work best in a PCB but can be used on a solderless breadboard as shown in this tutorial. The pins are normally open (disconnected) and when the button is pressed they are momentarily closed.
They come in a pack of 10, they're pretty handy so you'll want to keep them around.
You can find an EAGLE cad package for these in switch-omron:B3F-40XX