Assuming he is already used to a collar, it is time to teach puppy to walk with a leash. You can start this exercise with very young puppies. This is critical for your pup's safety so that he won't run out in the street or some other potentially dangerous place while you are walking him.

Try getting your puppy used to the leash gradually. Don't hook him up and immediately try to walk him as he will probably need to get used to just having the leash there first. Instead, sit on the floor and pet your puppy. Then very casually attach the leash and just let it lay there with your pup as you keep petting him, as if the leash isn't even there. Puppy will probably notice the leash and perhaps even go ballistic over it at first – the idea is to gradually get him used to it. Allow him to run around with the leash attached fora few minutes (supervised so that he doesn't hurt himself). When he is calm, disconnect the leash and praise the dog. Do this for a few minutes, several times until he readily accepts the leash as his friend. You can do this in a day, or stretch it over several days if you like.

Once puppy consistently accepts the leash without a problem, you can teach him to walk with it.