This video goes over how to create GUIs in Skript, how to handle events such as inventory click and close, and then how to implement a simple cookie clicker style game.
Code: https://gist.github.com/underscore95/8dfcf234891e480dd200943e7fcda493
Mentioned Tutorials:
Items:
I noticed I didn't really explain what the second issue was, essentially when reopening the gui we were setting the tag to tutorial-gui but opening an inventory when one is already open closes the previous one so the tag was being deleted, and the fix is to set the tag after you open the GUI.