You can only connect 1 external monitor. This is because the card can only use 2 outputs at a time, and to my knowledge, there is no way to disable the laptop's screen.
You can do something like play games on the notebook screen and do other things on the other screen but you will have to ALT + TAB out of your game, or hit WIN or something since the mouse can only work on 1 monitor at a time. If you move the mouse to the external monitor with a full screen window open on the laptop such as a game or movie, and click something on the external monitor it will minimize whatever you have open on the laptop monitor. Kinda sucks but that is the way it is.
I am currently using the laptop's monitor and have my external monitor connected to my desktop. There is a way to connect my laptop the the external monitor as well but I don't see the point since my mouse and keyboard is connected to my desktop. At school I will be using my external monitor on the laptop though since I'm keeping my desktop at home.