The Window Handle can be used to identify a window and manipulate it through the Windows Actions (UI/WIndows > Windows).
In order to store the handle of the window into a variable, use the "Run Application" Action with the input "After Application Launch: Wait for Application to Load".
The window handle is a unique number that identifies the window.
Now that we have the handle into a variable (%handle%), it can be used by the Window Actions (Focus Window / Set Window State / Set Window Visibility / Move Window / Resize Window / Close Window).
This is useful in case the automation is opening several windows with the same title/class and it is difficult to distinguish them.