To leash train a puppy, you can start by introducing the puppy to the leash and collar gradually inside the house. Let the puppy get used to wearing the collar and dragging the leash around under supervision. Then, you can start short walks in a quiet area to help the puppy get used to walking on a leash. Use positive reinforcement like treats and praise to encourage good behavior while walking on a leash. It's important to be patient and consistent with training to help your puppy learn to walk nicely on a leash.