Basic Commands
The four basic commands are "Come," "Sit," "Stay," and "Lie down''. Once your dog reliably understands basic obedience, it is ready for walking to heel. It must understand "Sit" because this is always the takeoff point for walking to heel.
Traditionally, dogs are trained to walk by your left side. (The dog is always at the handler's heel, which, of course, is why training is called "heel" training.) It really does not matter whether you start heel training on or off the leash.
It is not an issue of right or wrong, but rather what feels best for you and your dog. When a puppy willingly follows you off leash, it is easy to graduate to walking-to-heel training on a leash.
Use a leash with a bolt-snap of appropriate weight for your dog. If you have not introduced the leash before, let your puppy look at it and smell it.