You mean you don't have the /window command in your mIRC help file? I suggest redownloading mIRC from
www.mirc.com then.
In brief:
/window @windowMakes a window called @window
/window -d @windowMakes a window called @window on the desktop
/window -c @windowCloses the window called @window
There are many many switches, redownload and install mIRC then type
/help /window.