The Repository tab provides access to all your tables, fields, business objects, controls and programs.
The left pane also contains a Favorites tab in which you can store all your frequently accessed items.
If you need more space, you can hide the navigation buttons under the tabs, leaving a toolbar below.
The pane is docked on the left by default, but you can float the tabs or dock them on the right.
You can use the Tabs dropdown in the Home ribbon to display the Repository and other tabs.
For more information, see Repository / Business Rules Engine.