To Close an Application Window
Closing an application window removes it from all workspaces. Closing an application is the same as quitting an application on other systems.
Before closing an application window, save your work. In most applications you can do this by choosing Save from the File menu.
Choose Close from the application's File menu.
Or, double-click the Window menu button (in the upper left corner of the application's window).
Press Alt+Tab to move the highlight to the window you want to close.