Windows 8 and Windows 8.1, like Windows 7, makes very is easy to set up dual monitors. You can add a second monitor by using the following procedure.

Setting up two monitors is useful and convenient when you need to change the display settings during your presentations with a projector connected to your laptop.

Connect the second or external monitor to your computer first. Then press Win+P. This will open the Charms bar.

Select the Extend option.

That's it!

Related read: How to setup Dual Monitors in Windows 7 easily