The information isn't always clear online (ex. how big the tour size is, type of vehicle, how many stops, if you can get out of the bus, etc) but it does give the general overview so you kinda know what you are getting into.
When you pre-book once you board the ship your tickets will be waiting for you in your room. Check them over to make sure the dates, amount of tickets, and tour are correct. Also read them over so you know what time and where you are meeting as well as any recommended clothing / items to bring as they will be mentioned here.
If anything is incorrect or you are unsure of anything on the tickets make sure to call down or swing by the Shore Excursion Desk as they will be able to assist you.
The nice thing about pre-booking through the cruise line is that you are guaranteed space on busy tours and if there are any cancellations or port changes due to weather or instability then you will be fully refunded (depends on how you paid). These pre-booked tours also guarantee that you will be back on the ship before it departs or else the cruise line will take care of the cost of you making it to the next port to meet up with the ship.
