This area of the environment is actually two separate sidebars which flank the graphics area. However, each sidebar can be toggled on and off separately, so you might only see one — or even none — at a time.
Turn the tab area sidebars on and off by selecting left side, right side, both, or none from View > Tab Locations.
Each tab area sidebar can contain multiple complex features, such as the Utility Menu, and Model Browser. To maximize available space, multiple features are organized onto tabs; click a tab heading to bring it to the forefront.