Need Help Talking to NPC

Hey guyz i have a question, im recently creating an rpg game. I want the hero to be able to interact with all the characters in the game. But i dont know how to do that. So I was wondering if someone could help me out maybe a tutorial or somthing. Well this is how it should go: the hero speaks with the NPC (granny) with the ENTER Button, then a box should pop out infront or on top of her with some texts saying hello, how are you? Can somone please help me, what’s an RPG game without it. Thank You.