The exact boarding process of your expedition cruise will vary from operator to operator. Once you have booked a cruise, we will send you a briefing from your ship, detailing all the steps. If you have chosen a ship-based expedition cruise (in contrast to Air Cruise, where youre being flown into the destination) , then typically you can drop off your luggage on the first day, and the crew of the ship will take care of transporting your luggage to the ship, and will even place it in your cabin for you.
Here is a video that Benno, the founder of Polartours, recorded in Ushuaia to talk you through the process: