At the moment you still cannot pre-book excursions online. It is still in the process of being done and getting the bugs worked out of the sustem. You can book through your TV on most of the ships now if not all of them. Not sure if the system has been installed fleetwide yet or not. IN any case, if you cannot book on the TV just fill in the form that will be waiting for you in your cabins and submit it to the Shore Excursions desk as soon as possible.