NET2FTP!
This tutorial shows you where to go after you have made your sub domain.
This is fairly easy to catch on to.
Step One
Okay, so first, you need to get the info from your ftp account.
Once you have it, Go to https://webftp.dreamhost.com/
Lost? Click here.
Step Two
Once you've gotten there you will see the log in.
Get the info from the FTP Account, and match it up with the log in fields.
Leave the "Initial Directory" field blank.
Lost? Click here.
Step Three
And you're done! Easy, right?
Click here to check out how to edit your sub domain.