Stay is the opposite of Come. Instead of Fido coming to you, you come to Fido. It means to remain where he is until you come to him and release him. For the dog in the picture, it means stay on that newspaper. Therefore, we never call our dog from a stay.
The most common mistakes made when teaching Stay are 1) calling the dog off the Stay and 2) taking too many steps or pausing too long too soon.
1) Dogs will anticipate your next cue and break the stay if they are used to being called from the stay. This will cause them to fail the CGC test and make it harder for you to get them back should they get loose. Learning that Stay means I don't move until mom or dad comes to me could save your dog's life!
2) If you take too many steps away before your dog is ready, they will learn that Stay means "get up, then sit back down, then get up again, rinse and repeat". There is never a time in real-life when you will tell your dog to stay and then stand still looking at them for several minutes (unless you do competition obedience). In real-life, you will be moving while your dog stays still, so it is better to teach Stay with you in motion.