All POS software is different, and any software and equipment you purchase should come with setup directions and support. General guidelines are to program the buttons to reflect your merchandise in a way that's quick and efficient for your cashiers to use. If customers need to sign on the device, make sure you can quickly flip or move the display for customer access. The primary function of your POS system is to correctly and rapidly sell products and serve customers, so make sure your setup facilitates that.