Everyone starts somewhere
Just copy and paste this:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
On Error Resume Next
    If Target.Address = "$D$7" Then
         
        user_name = InputBox("Please enter your Oracle user name:")
        If user_name = "" Then End
        Oracle_password = InputBox("Please enter your Oracle password:")
        If Oracle_password = "" Then End
        end_date = Format(InputBox("Please enter the period end date in the format dd/mm/yyyy (eg 30/06/2013):", Default:=Format(WorksheetFunction.EoMonth(Date, -1), "dd/mm/yyyy")), "dd/mm/yyyy")
        If end_date = "" Then End
         
        Range("N10").Value = user_name
        Range("N11").Value = Oracle_password
        Range("D7").Value = end_date
         
    End If
On Error GoTo 0
End Sub