You want to plant yourself in place with the puppy on the leash in the place you want them going to the bathroom. It isn't about playing, but you can let them play if you have time and they are finished going. Never let them play before, but if you do don't take the dog inside immediately after he finishes because the dog learns that as soon as he goes the fun is over.
Every time the dog goes to the bathroom you say "good potty" or "good get busy" or whatever you choose to use to praise the behavior just make sure you stay consistent when you do it. Say it over and over again as they are going. Do it every time. I still do it with my lab who is 8 years old. Pretty soon if you say go potty or get busy or whatever you chose, the dog will go on command.
Its great for those days when its cold or rainy and you don't want to be out long waiting for the dog to do its business.