I was thinking about this and realized as a newbie you may not know the boarding process, I didn't my first year.
When you get go the port, you'll see piles and piles and piles of luggage on the ground. You'll get official MSC luggage tags (the sticky paper kind like airlines use to tag your bags) that you need to put your name and cabin # onto, and affix to your luggage. You drop your bags off outside with the many many porters that are there to take them and put them into those piles. Then you go get into the line (with any carry on bags you might want to have with you) and go through the lines... first stop is security screening, much like getting on an airplane, you put your carry on through the scanner thingy and walk through a metal detector. You then move to the waiting area (seats) where you fill out your health questionnaire. The staff directs one row of seats at a time to enter the line to get on board. Your next stop is with the MSC registration folks, who ask for your IDs and credit card and take your picture to get you officially booked into your cabin and provide you with your 'sign and sail' card that you'll use for all transactions on the ship - it's your room key and it's how you pay for anything the ship sells (anything except JamCruise Merch). That's the last stop! Once you have your card you make your way over and up the gangplank, and show your sign and sail card to ship security as you board!!
Now go buy drink tickets, find your cabin, and decorate your door
that's what I do anyway!
Your bags will appear outside your cabin door sometime later the first day, I've had bags show up before I first got to my room, and I have had them show up at like 1am... so it's very variable when your luggage will get to your cabin that first day, pack your carry on with this in mind