Press the small arrows on the left or right side of the screen. From this quick menu select the pen icon. 

When the pen icon is selected this allows you to freely annotate anywhere on the screen. 

You are able to save your annotations in the same way as the CommBox Whiteboard application. You have the option to save locally to the CommBox internal storage or to a USB as a PNG or PDF file. You are also able to share the annotations via a QR code.