Game help

i’m making a pokemon style rpg, i’v got the sprites, and the code to control the character and also how to stop them goin through stuff, but im confused on how i can make them interact with other character i.e talk to a NPC or read a sign. i figured that there must be an invisible movieclip to tell flash that the character is in range but how do i go about making the text appear and change?

also if possible is there a way that you can make random battles happen say when you go through long grass.