How do I make it so that when you talk to a NPC then it shows a different screen?
From OHRRPGCE-Wiki
[edit] If you meant showing a backdrop behind the textbox...
In the Box Appearance submenu of the Textbox editor, select your Backdrop.
[edit] If you meant changing map...
Add a door somewhere on the map where the player can't reach it and link it to a destination door where you want to teleport the player to. In the Edit Conditionals screen on the Textbox editor set DOOR: Always do the following and instantly use door X.