Domain Name Servers, or DNS for short, are basically the backbone to the internet as we know it. Without DNS servers, human interaction with the internet would be extremely difficult.
Let me explain. Computers only understand numbers, such as in an IP address like this one: 192.168.1.1. Humans however, tend to have a difficult time remembering numbers, so this is where DNS servers step in. They make it possible for you to type into your browser www.google.com and it translate that name into an IP address. This then tells your browser where to look for www.google.com and where it is located.
What Are A Records?
Now that I've explained the way DNS servers work I want to explain the difference in A records and CNAME records, as I see these two getting confused a lot lately. A records match up a domain or subdomain, to an IP address. DNS servers use A records to tell them where to point to for your naked domain. In layman's term's: if your domain is www.coolstuff.com, then your naked domain is coolstuff.com. So your A record for coolstuff.com would look like this:
Confused yet? Let me explain what all of this means. The @ under the Host column, tells DNS servers that it is using this for the naked domain, in this case coolstuff.com. The IP address in the Points To column, tells DNS servers where to find your naked domain at.
What are CNAME Records?
CNAME records are a little different. CNAME stands for canonical name and they are used to alias one name to another. For example, you can have multiple services running but you want them all to point to one IP address. So you could have mail.coolstuff.com, ftp.coolstuff.com, and www.coolstuff.com all pointing to the A record for coolstuff.com, which points toward whatever IP address you have you A record set for coolstuff.com. So, your CNAME records may look similar to these:
A Word of Caution
You can only have one A record, per domain. Normally there is no need to edit your A records, as these are normally done for you by your registrar. A records must always have an IP address to map to as well. CNAME records only need a domain name to point to. You should never use a CNAME record that points to your root domain name.