If you are like me, application-heavy and network-light, then DNS is a relative mystery to you. A friend (network guy) gave me the following high level explanation.
You type and enter an address into your browser, e.g. http://diablopup.blogspot.com.
The first thing that happens is your computer asks your ISP's (e.g. AT&T's) DNS server (1) "do you know the IP address for this website?" If it does, it will tell your computer what it is, and you connect directly to the Website Server (3).
If your ISP's DNS server doesn't know, it will ask (in a roundabout way) the website owner’s DNS server for the IP address(2). Then it connects to the website server (3).
Once your ISP's DNS server knows the IP address, it keeps it in cache so it doesn't have to ask again, thereby making the connection quicker on subsequent requests. This is why you sometimes experience a slow page load when visiting a website for the first time, but then witness quicker connection on subsequent visits.
There are more "nuts and bolts" to DNS, but this is an intuitive picture for people who can't work with DNS directly.