First, have you had a look at the tutorials that are pinned?
To make the NPC, you just go to the NPC tab, right-click > New. Set their class to publican. Look at the scripts on the publicans that exist already (They all follow this convention: Pub_City_PlaceName). You'd pretty much just copy that, and change the global variable (Rent_City_PlaceName) and door (Rent_City_PlaceName_Door) referenced in the script to ones for your inn. Global variables are found in the Gameplay > Globals menu. The script editor can be found there as well, or by clicking on the pencil button.