The Catalog's graph helps visualize the whole app and how it transitions from one page to another. The wizard displays all the page's thumbnails and the page's interconnections graph to show how the transitions work. You can click on any page to make changes. Each page is associated with actions that define how the given action will take the user to the next page.
The graph's sub-section shows the pages that are close to the page being edited. This feature lets you go to neighboring pages from the editor window itself.