How to be a free-domain provider

[hirikarate]

Nowadays there are a lot of free-domain services but the top-level-domain is strange: .tk, .9x.com, .cat.com, .blahblah.net.
How can they do that? If I want to be a free-domain provider, what should I do? What do I have to pay? :goodbad:

[alvo]

What you're referring to are subdomains. They're set up within a domain name itself, so everything is somedomain.com, and appended to that URL is the subdomain name, so you can have something.somedomain.com and somethingelse.somedomain.com and so forth. Here's how it works with the Apache web server: http://content.websitegear.com/article/subdomain_setup.htm