The 'Item List' presents all the Items that book can interact with. It doesn't mean the player will have these when he starts to play, for that you need to apply an Item Action. You can Manipulate the Items via the Items panel in the Book tab, or via right clicking on the list which will pop a menu of actions.

Items Toolbar
Add - Adds an item to the list
Remove - Remove the selected item from the list
Edit - Edits the selected item from the list

Adding an Item
Adding an item is quite simple. When the dialog is up just fill The following information:
1. Label: The name of the Item.
2. Description: The description provided when the player clicks on the item.
3. Usage Destination:
The page that the user will go to when directly choosing to use the item.

It will often be useful to use the "Previous" destination in pages that items leads to since you will want the player to get back on track. For example healing will show a message and then the player will go back to the story.