You need to specify the location and size as well as the window name. From the help file /help /drawcopy
/drawcopy -ihmnt @ [color] <x y w h> @ <x y [w h]> Copies part of a picture to a different position in the same window or to another window. If the second [w h] parameters are specified, the picture is stretched/squeezed to fit.
The -n switch prevents the display from being updated immediately. This allows you to make changes to the window in the background and then display the results only when you've finished. You can update the display by using any of the /draw commands with only the window name specified.
The -n switch is a switch that goes for all /draw* commands that do actual drawing, it is not strictly related to /drawcopy, and thus natural to be mentioned in the first /draw* command explained in the help file. Anyway, it's not important.