To get a Crew List, just set the subarea, then press Get or Add to Crew and Boat Lists. To add yourself to the list, first get the list for the subarea you want, then follow the appropriate "add" link.
A subarea is a relatively large area that boats depart from or cruise in, like Southern California or the Bahamas. Because of the nature of cruise crewing, a subarea should not be a single city. For now, a subarea cannot be a destination.