The Main Menu is made of 8 menus that allow the user to interact with Ardour, and below is a reference of all the menu actions.

Notice that a lot of these menus, and probably all of the most used ones, have keyboard shortcuts to make using them easier and faster. A summary of these shortcuts can be found on the Defaults Keyboard Bindings page, and every menu in Ardour can be reassigned to an user defined key binding, or used via OSC with a control surface.