First things first, you should have trained your puppy how to sit before attempting the stay command. Fortunately, you can use this same technique to train them to sit as well. Use common sense, instead of holding your hand out to make him stay, you should push your pups rear end down to make him sit. All other things are basically the same. On to the stay training.
First, make sure your dog is focused. It is better to train your dog before they eat so they are very willing to do anything for a tasty treat. Have your dog start out in a sitting position, they will be less likely to move from the start. As you back away a little bit hold your hand out and say “stay” in a commanding voice. If they move start over immediately. Then when you are ready for them to move either use the same word like “come” or their name in an enthusiastic voice. As soon as they reach you praise them with a massage or a doggy treat. Just repeat this training twice a day for as long as it takes.
Be sure to be patient with your pup. Some will get it right away, and others will take a bit longer. But they are anxious to please you so they will eventually learn. This also creates a bigger bond between you and friend so it is a great thing to do. Also, feed your dog healthy treats and keep your yard clean to keep him free and you free fromdisease.