Domain Name Service/System is a name resolution service that resolves Host names and fully qualified domain names (FQDNs) to IP addresses. For example, Cnet.com's IP address is 216.239.113.101. But you don't have to remember this number, only the name. That's the beauty of name resolution. When you enter the name in your browser, it attempts to resolve the name to its IP address by first looking in your DNS cache, then your Hosts file, and finally will contact a DNS server. You can open a command prompt and enter, ipconfig /all to see the address of the 2 DNS servers. If not present I suggest contacting your Internet service provider.