Out of the box the EyeX cannot be used like a common input to the entire PC. But included in the EyeX Installer Bundle there is a software called EyeX Interaction which provides certain EyeX functionality in Windows. This software is developed by Tobii and makes it possible to use EyeX with a number of applications in Windows 8.1, for example Chrome, Internet Explorer, Microsoft Office 2013, and Adobe Reader. What you can do in these applications is basically scroll and direct click using your eye-gaze and a designated key on your keyboard, the EyeX Button (by default mapped to the Right Control key). That is, you aim with your eyes but you control the action using a keyboard key. Also, the EyeX Interaction software enables some general EyeX functionality like scrolling and direct clicking items in the Start menu, switching between applications using your eye-gaze and teleporting the mouse pointer to where you are looking either when you start moving the mouse or when putting down a finger on your touch pad.
For example, with the EyeX Engine and EyeX Interaction software installed you can surf the web with Chrome using only your eyes and the EyeX Button. To scroll: look in the direction you want to scroll while holding down the EyeX Button. To open a link: look at the link and the tap the EyeX Button.
I hope this gives you an idea of what you can (and cannot) do with the EyeX Controller and EyeX software out of the box.