When you have done a booking, you will find it on your front page, and/or under Upcoming bookings.
Tap on Add booking
A calendar window will then open and you can edit the details (Subject at the top, invite others, agenda etc.)
Then press Add.
A calendar invite with your booking details will be sent to your default calendar (and those you have invited).
Make sure:
that you have chosen the right calendar to send your booking too. You can change this in the middle of the screen shown above.
Be aware:
that if you tap repeat your booking will not repeat, only your calendar event.
that if you want to delete your booking, you need to do this in the Orbit app. Deleting the event in your calendar will not cancel your booking.