Sets the keyboard focus to the specified window
#include <WinAPISysWin.au3>
_WinAPI_SetFocus ( $hWnd )
| $hWnd | Identifies the window that will receive the keyboard input. If this parameter is 0, keystrokes are ignored. |
| Success: | The handle of the window that had the keyboard focus |
| Failure: | 0, call _WinAPI_GetLastError() to get extended error information |
Search SetFocus in MSDN Library.