I need to export cards to Google calendar - how can I do that?

Before integrating with Google Calendar, make sure that there are due dates on some of your tasks.
To use due dates, go to the board’s Settings - Card Template and activate the Due date field.

Now, once you’ve set some due dates for tasks, go to the Tools menu in top-right corner of the board, and choose Export to calendar - Google.
In your Google calendar tab, you will see a pop-up asking: Do you want to add this calendar?
Click Yes, add this calendar - your tasks with due dates should get displayed in the calendar.

Please note, that due to Google’s policy on external calendars synchronization, it can take up to 24 hrs for the integration to activate.