You need to connect the monitor to the VGA port, it`s a big one with two external holes, where you fix the monitor
Then press FN + F5 (I have a Dell) and it will appear a case asking you how the monitor should work, all the time or when the display of the notebook is down and some other setting
If it doesn`t work with F5, try FN + any F key, it depends on the model of the notebook
