After setting the name servers for the domains to ns1.dreamhost.com etc, you need to add the domains to the DreamHost hosting system. You do this in the DreamHost panel at Domains -> Manage Domains -> Add New Domain / Sub-Domain, add them as Fully Hosted.
Once you have done this, new directories will be created in your home directory corresponding to the domains you have added, these directories will by default have the same names as the domains. You need to upload the site files for each domain into the relevant directory.
Note: After changing the DNS settings, it can take up to 72 hours for the changes to propagate across the Internet, during this time your domains may not be browsable, but you can still upload content during this time.
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