Can't figure out how to use this gui display mentioned on the plugin page, how do I set it up?

Edit: by set it up I mean get quests to show up in the gui, since that probably wasn't a clear question from above.

I can field this one...

1. target the npc you want to display gui by standing near them and typing /npc select
2. get the npc's id number by typing /npc id
3. do /questadmin togglegui (the npc's id number)

done- that should work

Volkenstein is correct. Toggle the GUI using the command with a specific NPC ID. When you do that, any Quests that have been assigned to that NPC will now show up in an inventory display when you right-click on that NPC.

Closing due to lack of response from OP