its the place under where you can put the custom lunch parameters in
like this for an example:
@ExileServer;@ASDG_JR;@hlcmods
Just remember that the last one not may have the ; at the end
Try take a look here and see if it makes it easier to understand
http://www.exilemod.com/topic/282-infistar-install-tutorial-101/
it isent so difficault when you just find out how it works