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DNS stands for Domain Name System and is primarily responsible for associating URL's, such as www.profitability.net, with IP addresses, such as 209.173.159.6.  Each device connected to the Internet is assigned an IP address, which works like a phone number for that device.  By using the IP address, any system connected to the Internet can access any other system connected to the Internet.  Since IP addresses are hard to remember, DNS was created as a method to use simpler names to refer to devices on the Internet.

The first part of DNS starts with your Registrar.  Domain name registrars are the companies, such as Profitability.net, that are able to sell you the use of a domain name for a specified period of time. Domain name registries maintain a database of contact information for each domain they are responsible for, as well as delegating authority for the domain to the relevant domain name servers via the root name servers.

Root name servers are servers that are distributed across the globe and are able to direct querying name servers to the authoritative name servers for any registered domains.  Each domain will typically have at least two authoritative name servers.

Authoritative  name servers often provide a number of services:

For domains for which it is responsible, it translates between URL's and IP addresses for anyone inquiring, through the use of A records.  In addition, the name server can also tell inquiring name servers where to send mail for domains for which it is authoritative, by using MX records.  For local users of the name server, it will query other name servers in order to get DNS information for domains for which it is *not* authoritative.

"A Records" are the literal translation between a URL and an IP address.  Anytime you visit a URL, your computer contacts name servers that are able to translate the URL you wish to visit into an IP address that your computer knows how to contact over the Internet.

"MX Records" describe where to send mail for a particular domain.  Typically there will be several MX records ordered by priority.  A mail server wishing to deliver mail to an address at your domain will try the highest priority record first.  If that attempt fails, it will try the second, and so on.