The 'Main Menu' is always on the left hand side of each GVO screen and allows you to move between the varies elements of the GVO - the Calendar (for meetings), the Board and Committee folders, the Policy area, Training Records, Tasks and the User (and Board) area. There are sections in the help system about all of these.
The order of the main menu and the folders that are on the main menu can be changed by your local GVO Manager (new menu folders can be added if required).