(1). What is GetWindow(); and how do I use it?
(2). How to get the object on another HWND(window)? How to declare the object?

Amplified:

(2). GetDlgItem(Hwnd2,EDIT2);
{ Hwnd2 is another window, not under my control, I didn't create it, how do I get EDIT2 on Hwnd2? Everytime I try to use this command it returns an error: "EDIT2 not Defined". and if I defined it, still I cannot get the control EDIT2. }
{ I used FindWindow() to obtained Hwnd2 and I know there's an object on Hwnd2 called EDIT2 }