You can use the key based Gaze Scrolling anywhere you can scroll with your mouse wheel.
Just look where you want to scroll and press the "Page Down" key to scroll down or the "Page Up" key to scroll up.
If you want to lock the scroll position, press the "Page Up" and "Page Down" keys together. A small blue circle will be displayed at your gaze position and as long as it is displayed, scrolling will continue in this scroll area regardless of your gaze position.
You can remove the lock by pressing both keys together again.
Note: As long as NUIA receives gaze data, the normal functionality of the Page Up and Page Down keys is overridden. If you need these keys in an application, you can disable the key based Gaze Scrolling for that application via the app specific settings.