Classic menus are the traditional way of navigating the software that use drop-down menus from the top of the window.
To enable the Classic menus, right click on a blank area of the toolbar and select Show Classic Menus. Selecting Show Classic Menus a second time will hide the Classic menus.
To access the Classic Menu commands without displaying the menus at the top of the window, right-click a blank area of the toolbar.
See Basic Elements of Your Software for a diagram of the main window.