When document windows are minimized, an icon for the minimized file(s) will be created and placed in the viewport behind the windows currently open. The Arrange Icons function is used to arrange the minimized file icons in an orderly fashion. Note that the icons will not be visible if one or more files are currently maximized.

Before:

In the example below, all three open files have been minimized, and their window icons appear in the viewport background in no discernable order.

After:

In this second example, the Window>Arrange Icons feature has been used to arrange the window icons in a more orderly fashion.