Your events are kept 'as is' in your iPad, they won't be imported or mixed with the app's data, it is only a convenient feature that will show your diary/planner data and your planned events together.
How to enable this optionYou can grant or revoke the permission to access your calendars from the iPad's setting app.
How to choose which calendars to integrateFrom iDoceo's main screen / Settings /Calendars you'll be able to enable or disable your calendars
How to integrate with Google CalendarsYou must first add your gmail account as a calendar provider.
The details explained here http://ipadinsight.com/ipad-tips-tricks/how-to-sync-google-calendar-with-the-ipad/