Official Dreamhost Guide can be seen HERE
or you can find it under Goodies -> MySQL Databases:
What you will see on the next page:
To get your Database password for the Database User , click your user. On the next page you will be able to retrieve your password:phpMyAdmin is where you will log in. Your domain has to be hosted with dreamhost. All of the Hostnames are all interchangeable, so you do not have use use one specific to your domain, just a hostname setup.