I want to register a domain name and there are a couple of things I do not understand. One can register second level domain names on the Internet, such as example.org, for a small fee. Upon registration you should supply addresses of nameservers. Can any publicly accessible host become a nameserver, or they should be registered with ICANN? What do people usually use as nameservers? Let's say that my example.org is pointing to 1.2.3.4. Now I want to create a third level domain, ftp.example.com, pointing to 1.2.3.5. Where do I put the "ftp" in? Does this action require access to the nameservers, or another (paid) registration is necessary?