They enter several codes into their encoders on SAM;
the codes include the Port (created by the ShoutCAST Server), IP Address (also created by the ShoutCAST Server), and then there's the password (created by the Administrators).
All of the above are set-up through several things on the cPanel (Control Panel); such as radio stats, which displays how many listeners there are, what song is playing, and who the DJ is.
Basically, to sum it up, you buy a ShoutCAST server, you get the details of the server such as port and IP Address details, and the default password; you also get details to go in and change the password and IP address if you wish. Then you post the details on your site, usually located at /djpanel, for example; myhabbospace.net/djpanel. The only way you can get the details is by an Administrator of the site creating you an account.
Now, on SAM, you enter all of the above details, and more. Such as, DJ Name, what type of music you play, and more.
There you go. (: