In competition obedience training, “heel” means the dog is walking on your left side with his head even with your knee while you hold the leash loosely. Puppy training can be a little more relaxed with the goal being that they walk politely on a loose leash without pulling. Some trainers prefer to say “let’s go” or “forward” instead of “heel” when they train this easy way of walking together.
Just as a child needs a caring parent; an athletic team needs a coach; your puppy needs a leader and a clear social hierarchy. If you do not take up the role of leader, your dog will; and you will end up with an unruly, disobedient dog. Many people try to win their new puppy's love by letting the puppy always have its way. Buckets of affection is a wonderful thing for most puppies, but it must be tempered with respect.