The argument he refers to is called a 'callback' parameter, or variable. For example, I've re-written the initialize method for Lambchop's Super Simple Journal script to accept an optional argument
class Scene_Journal
def initialize(callback = 0)
@callback = callback
In the method where the escape/X (Input::B) key is pressed, I check the callback parameter & call the appropriate scene
if @callback == 1
$scene = Scene_Menu.new(4)
else
$scene = Scene_Map.new
end
This is to accommodate calling the scene from either the map, using the Q (Input::L) key
$scene = Scene_Journal.new(1)
or calling it from the modified menu
$scene = Scene_Journal.new