If you have already clicked the "Join" button, filled out the information, and remember the login and password you selected then click on "Manage My Cruise" at the top of the page. Log in with the username and password you selected. You will need to have your "confirmation number" to pull up your cruise. This number will be on the confirmation you received from your travel agent.
Once you do this you can go through the online process to fill in your cruise documentation.