You can grab our iCal feed URL from the settings page (top right corner, gear icon) on Todoist.com. From there you can add that to Google Calender (website version) from the Other Calendar menu on the left hand side.
This will then sync with the one on your android device. I believe the app on Android can add feeds as well, through it's menu system, though it's more complicated.
so this is a premium feature only? cant do with free account, is that right?
Yes, Google Calendar integration via an iCal feed is a premium only feature.
The calendar app correct?
We don't have a calendar app. What this feature does is it allows you to subscribe to an iCal feed of your Todoist tasks in Google Calendar. For more information about it, please refer to this video: https://www.youtube.com/watch?v=gzGubOy8GuE
Let us know if you have any further question.
You can also check out a different calendar: sunrise.am. It has integration with Google :-) Calendar and Todoist