Those on a 30 day free trail would be charged monthly at the end of the 30 day trail.
You will be notified about the first charge from 14 days before the first charge and if you wish to pay Quarterly or Annually rather than monthly you can update your payment to take advantage of the cheaper costs of paying quarterly or annually.
If you did decide to cancel just fill in the Hosting Cancellation form in your Client Area before the end of your free trail