First you'll have to create a MySQL Database on your hosting provider (Dreamhost).
After a MySQL database is created, you will be provided information about this same database:
MySQL DB Name
MySQL User Name
MySQL Host Name
Some of this information might've been provided by you while in the process of creating this database.
If you can't see your Host Name upon database creation or any of these information, contact your hosting provider (Dreamhost) and ask them to help you out find this information.