The Main Menu window is a custom window that contains several buttons that allow you to togle the display of various windows.
The window will appear when you right click on the right most button in the Status Index window or the button labeled "Main Menu" in the Command window of the user interface. The version of the user interface you have loaded is shown at the top of the window along with the link address to the user interface homepage. The current real and game server times are shown at the bottom of the window.
There is nothing shown when the window is concealed. The window is invisible with no graphics or controls to minimize the amount of memory used. Nothing will appear on the screen when you attempt to activate the window.