Click the tab that says 'Items', then 'Create New Item'. Put in the title and description. Below, there should be something that says 'Page Found on' you can guess what that does. Then there are the number of uses, can it be dropped, and picture options. Again, you can guess what those do.
Item effect right below that is where you chose a page that if the player uses the item on, they are taken to another specific page. You can do this with any number of pages; it isn't limited to just one situation of item use. There is also Default Item effect, for anytime you use the item, and Item scripting where you can make it so if a variable equals a specific number, and the item is used on a specific page, then you go to a certain page.
Edit: Don't forget to save the changes on the item before going somewhere else. Like the Story Properties.