He shouldn't be walking anywhere outside of your home/yard until be is fully vaccinated.
Until then, let him wear his harness and leash around the house and get used to it. Hold the lead loosely and walk in front of him- call him to follow you. He will learn to follow behind you. It really is a step by step process. He had to get used to the lead, get used to walking, etc. At his age, it's difficult because he can't go on legitimate walks, so it should be more about positive reinforcement with the leash and harness and teaching him to follow you.
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