Choose a box that can fit a webcam and be at a good working height for you. A wooden box is preferable, but any box will do. If using for a permanent installation, a projector may be useful below the 'screen'. Make hole at base of box wide enough for the camera cable, (and projector cables if using one). Secure camera facing up in box base, along with projector and front surface mirror if the throw distance is too long. If it is too long, then mount the projector up near the screen, with the mirror next to the webcam on the base of the box. Thread camera and projector cables to computer. Secure a piece of acrylic to open side of box. Then place a piece of paper the size of the acrylic over it. This provides a hard surface to work on, and can also improve tracking performance, whilst providing a projection screen. Activate touch screen software. Community Core Vision is a good one, as is Touchlib. There are others, but these two are the two main ones. Test settings, camera focus, lighting.