The Window menu deals with the layout of the different windows, and their visibility.

[] Audio/MIDI Setup
Shows the Audio/MIDI Setup window, where the sound system configuration can be modified
Editor
Show
Switches to the Editor view
Hide
Hides the Editor, hence showing the Mixer when the windows are attached
Attach
If the Editor window is detached, separated from the main window, attach it back
Detach
If the Editor is attached to the main window, fetach it (makes the Editor a separated window, usefull for multi-monitor setup)
Mixer
Show/Hide/Attach/Detach
Same as for the Editor, for the Mixer window
Preferences
Show/Hide/Attach/Detach
Same as for the Editor, for the Preferences window
Meterbridge
Shows the Meterbridge window, that displays all the tracks' meter at once and their recording status, and is very handy for multitrack recording
Scripting
Opens the Lua Scripting window, allowing to edit and run Lua scripts
[] Tracks and Busses
Opens the Tracks and Busses window, which is a shortcut to many tracks/busses operations (routing, effects, …)
[] Locations
Opens the Ranges and Marks window, a single point of control for all range and location markers
[] Binding Editor
Opens the Key Bindings window, which allows for easy creation or modification of any keyboard shortcut
[] Bundle Manager
Opens the Bundle Manager window, allowing to create and manage Bundles, which are a way to simplify connection management, by defining groups of ports
[] Big Clock
Opens the Main Clock as its own separate (and huge) window, which is helpfull when recording
[] Video Monitor
If a video has been imported in the session, opens a video window (namely, Xjadeo), synced to the timeline
Midi Tracer
Opens the MIDI Tracer window, allowing to follow each and every MIDI message entering or leaving Ardour
[] Audio Connections
Opens the Audio Connection Manager window, a way to make connections to, from and within Ardour's mixer
[] MIDI Connections
Same as above, for the MIDI connections
[] Log
Shows the Log window, where Ardour lists usefull information, warnings and errors