Option Explicit
Private Declare Function SetCursorPos Lib "user32" (ByVal x As Long, ByVal y As Long) As Long
Private Declare Sub mouse_event Lib "user32" (ByVal dwFlags As Long, ByVal dx As Long, ByVal dy As Long, ByVal cButtons As Long, ByVal dwExtraInfo As Long)
Const MOUSEEVENTF_LEFTDOWN = &H2
Const MOUSEEVENTF_LEFTUP = &H4
Const MOUSEEVENTF_MIDDLEDOWN = &H20
Const MOUSEEVENTF_MIDDLEUP = &H40
Const MOUSEEVENTF_MOVE = &H1
Const MOUSEEVENTF_ABSOLUTE = &H8000
Const MOUSEEVENTF_RIGHTDOWN = &H8
Const MOUSEEVENTF_RIGHTUP = &H10

Private Sub Command1_Click()
'активизируем нужное окно
AppActivate "Untitled - Notepad", True
'устанавливаем положение курсора
SetCursorPos  10 ,  10 
'клик
mouse_event MOUSEEVENTF_LEFTDOWN Or MOUSEEVENTF_LEFTUP,  0 &,  0 &,  1 ,  0 
End Sub