how to make npc in terraria?

Answer 1

They appear after all the requirements for their appearance are met. For example, for the Merchant to come you need to have 50 Silver Coins on you. Also, each one of them needs a separate and properly built house.

A proper house is: at least 5 blocks high, 7 blocks wide building with a backwall, a table, a chair, a lightsource and a door. And no dirt.

Cheers!