The window manager interface contains the functions that create, move, and alter a window, the most basic element in a Windows application. A window is a rectangular region that contains graphic representations of user input, input options, and system output.
Windows is a menu-driven environment; menus are the principal means of presenting options to a user from within an application. The functions that create menus, alter their contents, and obtain the status of menu items are also part of the window manager interface.
The window manager interface also contains functions that create system output. An example of this output is the dialog box that applications use to request user input and to display information.
The window manager interface also contains messages and the functions that process them. A message is a special data structure that contains information about changes within an application. These changes include keyboard, mouse, and timer events, as well as requests for information or actions that an application should carry out.