oh, ok, you want to know how to actually make a screeny.
ok, with the window open, make sure it has focus, hit Alt & PrintScreen at the same time, then, open Paint, go to Edit and select Paste. It will paste the screeny for you. Then, go to File -> Save As, type a name for it and from the dropdown box select JPG.
Now, paint for some reason saves the extensions in upper case, remember that, when you enter the url, i.e.
http://thissite.com/images/screeny.JPG, make sure it is written correctly with the case correct or it wont show.
Hope this helps!
P.S. Alt & PrintScreen will copy the window that has focus, PrintScreen by itself will copy the entire desktop.