It's all taken care of when you check in to your Disney Resort. They'll check your passport or other ID there, and you'll get your KTTW card, which gets you on to the ship and into your stateroom.
So when you get to the terminal, you go through the security checkpoint, up the escalator, and right through the terminal and onto the ship. Although the terminal is just stunning (including the big scale model of the ship), so take a minute or two and look around. Then giggle quietly at all the people standing in line over at the check-in.
Easy as pie. mmmm...pie...