nb=NotebookCreate[]; (*Create a window and store in a variable*)
nb===nb2 (*test for equality with another window object*)
SetOptions[nb,Visible->False](*Hide*)
SetOptions[nb,Visible->True](*Show*)
NotebookClose[nb] (*Close*)
SetOptions[nb,WindowMargins->{{x,Automatic},{y,Automatic}}](*Move to x,y screen position*)
SetOptions[nb,WindowSize->{100,100}](*Resize*)