try this site www.shipjobs.com
You probably want to start out on a mass market line such as RCCI or Carnival, as the luxury lines like Crystal only hire those with experience.
You don't have a choice as to what area of the world you'll be working, and you won't have a choice as to which ship you're assigned. If you get hired, you will be assigned a ship---and since you will be low person on the seniority ladder, you won't have much of a choice about anything. The luxury lines seem to prefer some college education in the area of the hotel or service industry.