Overlay Toolbox
The Overlay Toolbox contains controls for setting the data to be displayed on structures and in charts. It also contains identification information and controls. A small circle on the left of the identification is dragged to change the amount of space allocated to the identification section.
 
By default, the Overlay Toolbox is attached to the bottom of the Workbench Window, under the Viewing Area, in a horizontal configuration (top image).
It can also be attached to the left side of the Viewing Area, in a vertical configuration (bottom image, set in View menu >  Overlay Toolbox). Either configuration can be detached from the Workbench Window by left click + drag on the top of the Overlay Toolbox. To reattach, double click on the top of the Overlay Toolbox.

There are 4 tabs in the Overlay Toolbox, each controlling a different type of data viewing:
Tabs and files available for viewing change depending on whether you are in Chart view, Montage view, Volume view, All view, or Surface view