We're going to add buttons to the project from the previous chapter, to allow users to change the way the RGB LED works by pressing buttons. When you look at a button, you see four prongs. While there are four prongs, there are only two input/outputs to a button—one where electricity goes in, and one where it goes out when the button is pressed. This is because a button essentially controls the flow of electricity. When the button is not pressed, the contacts are not connected and electricity cannot flow, and when pressed, a conductor bridges the two sides and electricity flows. This is how we will use the button as an input device: a high signal means the button is pressed, a low signal means it isn't.