You will receive your cabin key when you check in. Your boarding card is your cabin key.
Your cabin number is at the bottom of your cabin key with the first number indicating which deck your cabin is on.
You will be issued with a cabin key for every passenger. If you're travelling as a foot passenger, you'll need to show your cabin key when you embark on the ship.
If you lose your cabin key at any point, you will need to go to the information desk to have it re-issued.