So far, so good. At this point, you should be able to see the domain in the Control Panel -> Domains -> Registrations screen. You can also check to see that the domain was in fact registered by checking any whois lookup facility to see what is listed for that domain (http://betterwhois.com/ is as good as any).
The domain will not “magically” appear in your Control Panel -> Domains -> Manage Domains screen just because you registered it. Registration and hosting are two different things. If you see the domain in your registrations section, and whois shows it is registered, then all you have to do is “Add a Domain /subdomain” in the “Manage Domains” screen, and DreamHost will set up hosting for it.
After some time (for DNS to be updated) your domain will be visible from the web.