You'll get two tags for each person...Just use those tags on your checked luggage, you don't need any for carry-on. Also, if you are flying into the port, put the cruise tags on after you pick up your luggage at the airport.
You will fill out a form or tell your cabin steward the time of your departure flight. He will then deliver colored tags at the end of your trip to use when you leave. Note the color of your tags as this is how they call you to leave the ship. You cant leave before your color is called. Its pretty systematic and well organized in my opinion. You will have to put your luggage outside your cabin the night before by a certain time. You might want to throw in an extra bag to keep with you for the clothes you wear the last night and anything else. You hold onto your carry on luggage. What I do is when I retrieve my luggage, I just dump the extra bag/stuff into it.