Now, a DNS server does two things. First it contains information about some part of the entire DNS database. The second thing a DNS server does is to act as a 'super-duper' resolver and find the answers to any DNS query that an ordinary resolver running on a PC might ask. So if some PC were to ask our DNS server to lookup the IP address for FTP.UU.NET, it would do so and return the results. You may have noticed that domain names have a hierarchical structure to them.
Dots separate the parts of a domain name.
The hierachical structure of domain names serves two purposes. First it gives humans a rough guide to the type, and maybe location, of the organization a name is associated with. As I said above, each DNS server maintains information about a piece of the entire DNS database. There are about 10 DNS servers in the world which maintain information about the top level, and some second level domains. You can now see how DNS servers handle queries about machines that they don't know anything about.