Once enabled, you need to create a structure with several hierarchical levels, and several sister pages in each level. and go to view one children page of the structure.
Then, when the user passes the mouse over a node in the line indicating the path to that node in the structure hierarchy (the sort of breadcrumb line at the page header belonging to a structure), the names of all the children of that node will be displayed below the path to that structure node as links for easier navigation.