Chances are you already have a domain name registered with one of the several domain registrars and you have your website hosted somewhere else. (I always recommend you to have domains and web hosting in different buckets). When you had hosted your website, the hosting company would have given you something called name servers and asked you to configure it on your domain name. This basically does the job of pointing the domain name to the right server (That’s how it is explained to a layman). This is what I did when I got started as well.
But there is more to it. The name servers given by the hosting company do the job of converting the domain name to the relevant IP address. When you type in a domain name in the browser, the borwser looks up what the name servers are for the domain name and “asks” the name server for the IP address of the server. Once the browser gets the IP address, the files are loaded from the server which is hosted in that IP address.
This is similar to calling up a yellow page service and asking for a person’s phone number to contact him. The sooner you get the response, the faster you can call that person and talk to him.
If the name servers are not fast enough to fetch the IP address and give it to the browser, the website starts loading a bit late and affects user experience. Sometimes the name servers can be down due to a technical problem or too many requests and there will be no answer at all. That’s the time when you get the ‘Website Not Found’ error messages.