When your domain name is registered it is delegated to a pair (usually, although more than 2 DNS servers can be used) of DNS servers. These DNS servers hold DNS records which tell the Internet “world” the physical location of the web server that holds your website and the mail server which handles your email. The physical location of these servers comes in the form of an IP Address e.g. 202.37.101.1. As it would be difficult to have to remember the IP Address of every website we wanted to visit, domain names were created to make this task a little easier. So basically, DNS servers just translate the ‘easy to remember’ domain names into the ‘hard to remember’ IP Addresses, so that Internet traffic can be directed to your website or to your email address.
Every ISP on the Internet has their own DNS Servers which direct the people who are using that ISP to the location they are looking for. For example, if Xtra is your ISP, then you would usually use Xtra’s DNS servers to find the website you type into your browser address bar.