You haven't said which cruise line but it is the same for both cruise terminals; you drive to the terminal entrance and offload your luggage and passenger(s) there, the car parking area is on the opposite side of the road. There are times when your car is taken off to another area to be parked but all of that will be mentioned in your cruise information nearer to the time of embarkation. .... Neil.
You take your luggage to the waiting area by the side of the ship, porters will then empty your boot of luggage onto trolleys and take it away to board the ship, you just carry your hand luggage. Your car will then be taken away by a driver and parked in the car park for you. You will be given a pink slip for when you get back from your fantastic cruise. All there is for you to do then is walk through into the departure lounge, book in get your photo taken for your cruise card and board your floating resort.
Have a fanstastic time on your cruise.
Cannot answer for other cruise lines apart from P&O. You drive to the Terminal. Take your luggage out get out of car yourselves, luggage whisked away, car driven away by very experienced staff. Next time you see your cases they will be outside your cabin. Next time you see your car its in the car park only a short walk away from terminal. Beats airports anyday.
We went with Royal Caribbean In Sept 2008. You drive into port unload your luggage. Then you drive your vehicle to the car park.