Leash training should start with habituation to the collar. Put on collar at home, so Jack gets used to it. First, perhaps, he will try to remove it. Distract him by play or treat, and soon the pet stops to notice that on his neck he’s wearing something at all. Do not try to put on a leash at home, because it will attract the attention of the puppy by its novelty, and he will try to play with him.
Put a leash on the street, there are many distractions, and your Jack will not pay attention to it. Buy 5 meter tape roulette for walking on the street.
Short-meter leash for a curious Jack will not be enough, because he researcher, he is required to shove his curious nose into every hole. He just doesn’t walk up on a short leash. The roulette should be a band and not a rope, you can cut your hands with the jerks.
Please walk, keeping Jack on the leash until you are sure that he will come at the first call "Come!"
If the dog runs away from you, do not chase him. Instead, turn around and run away from him. He interprets it as a new game and threw himself after you. And when he runs up to you, do not scold him, and praise and treat him so he will know that approach to the host associates only with pleasant.
When he learns to obey you implicitly keep him off the leash, let him walk alone. During the walk sometimes beckon Jack to yourself and put on a leash. Then again, let him go. Don’t take your pet on a leash just before going home, otherwise he has to develop a logical connection: Leash means that walk is over. And he will try to get away from you, and will run around the yard little more.