Did you start the webmin daemon? I haven't used webmin in a *long* time, but IIRC, it has its own webserver that needs to be running. I also recall that it serves up HTTP on port 10000. So to pull up webmin, you'll need to use a URL like this:
http://aaa.bbb.ccc.ddd:10000
Of course, the webmin folks very well may have changed their methodologies in the 5 years since I've touched their product.
Webmin's great at first glance, but the best suggestion I could give you for learning linux is to *not* use webmin. Learning how to effectively navigate and get things done on the command line is an incredibly valuable skill. Once you learn this skill, you'll be able to get things done much faster than if you were using webmin. Just my $0.02, though.