DNS stands for Domain Name Service. Every time you go to a web site using a domain name, you are actually using DNS. Your request for that domain name goes to your local primary or secondary DNS server which is usually administered by your ISP. Your local DNS server check its records to see if it knows what IP address that domain points to. If it does, then it directs you to that IP address. If it does not, then it sends a query to the Root DNS servers.