If a project is enabled for Structure, you will see a new Structure icon on the side navigation bar. Clicking this will open the Structure widget on the Project Page.
...
When you open the Structure tab, the Single Grid layout is selected automatically. The panel displays the most recently viewed structure or the default structure for the current project (as defined in the Options dialog). You can quickly switch to another structure by clicking the structure name and selecting the desired structure.
Project Page Options
You can make the widget open with the structure that is defined as a default structure for this specific project.
...