Not exactly sure what you're asking, I'll try and cover the bases, if I've missed the mark, try again...
you can log into ssh with any user that has ssh allowed - not just FTP access as is default, you have to tick ssh for that user.
The address you connect to is just the Yourdomain.com. If you want to be able to access website files, you'll need to log into ssh with the user name associated with the domain in question. (Panel > Domains > Manage domain > edit will show you the appropiate user)
With the system here at dreamhost you don't get any 'supper user' that necessarly has access to all domains - you just have to use the appropiate user.
Also, check out the K-base for Telnet / ssh info.
Hope this helps.