KPager is very intuitive to use. This help is mostly not needed, but I will give here some instructions and hints to optimize use of the application.
If you have a window that you would like to move to another position, you can "Drag and Drop" (DND) it by pressing the left mouse button on its minimized view and moving the mouse to the new position, then release the button, and you are done.
Although this doesn't seems very useful by itself, it can be very useful because you are not restricted to moves within a desktop. You can then move any window from one desktop to another without even changing desktops.