A USB switch is a device that allows you to share USB devices among different computers. For instance, suppose you need to control 2 PCs. Rather than having 2 keyboards and 2 mice, a USB switch allows you to use a single keyboard and a single mouse to control both computers. You press a button on the switch to select which PC you want to control. But you still need 2 monitors...
If you only want a single monitor, there are switches that also switch between different video inputs. These are commonly referred to as "KVM switches" (KVM being Keyboard, Video, Mouse.) But KVM switches cost more money...
My understanding is this project allows you to use a plain USB switch and the multiple video inputs on your monitor to simulate a full blown KVM switch.