Research the DNS System

What does DNS stand for?

Domain Name System Source

In general what does the DNS do on the Internet?

The DNS associates various information with domain names assigned to every participating entity on the Internet, and more prominently it translates domain names to thier original numberical IP address. Source

Why is it referred to as the 'Internet Phonebook"?

Because each domain (or person in a phonebook) has a unique IP address (or phone number) and the DNS compiles all that information into one location. Source

What is a Root Name server and what does it do in the DNS system?

A root name server are the servers at the root of the DNS hierarchy. It directly answers requests for records in the root and answers by returning a list of the name servers for the TLD. This is the first step in translating host names into IP addresses. Source