If you didn't get your luggage tags in your confirmation email when you booked there is a stand outside where they will give you a luggage tag when you get there.
You then go in through the door through the metal detectors and drop off your luggage that you aren't carrying on and head up the escalator to the check in counter.
At the check in counter you need your reservation confirmation, your passport/birth certificate, and the credit card you are using for all your on-board expenses.
After you check in they give you your room key and you are good. Just as an added FYI. There are tables to purchase the alcohol/soda package, make your dining reservations, and make your excursion reservations in the terminal you have to make before getting on the ship.
They tell you when you first get there they don't start boarding until 1pm but they opened the doors at 11:30am, VIP packages first then the rest of us.