By definition, a domain name is simply a human readable form of an IP address. In function it is the destination that you type into a web browser in order to visit a website, such a www.google.com. Metaphorically, it is very similar to how you would scroll to a contact in your cell phone rather than manually dialing the person by entering their full phone number; the phone number would be an IP address and the saved contact would be a domain name. Always buy a domain with a reputable domain registrar.
In addition to looking up a domain by IP, Whois lookup can also help you validate your website code with one of several Domain and SEO tools including CSE HTML validator, W3C HTML validator and the CSS Validator. Each WhoIs tool identifies errors in your source code so that you can fix things like missing closing tags, errors in character encoding and more. No matter what DNS information you are looking for, WhoIs can help you identify anything related to domain names quickly and easily.
It's good to decide early on if you want to have a brand domain or a keyword domain. The benefit of a brand domain is that your domain will most likely be considered as trustworthy, and immediately shows visitors that it's linked to your business or personal blog. A keyword domain, on the other hand, has the advantage that it will be better optimized for search engines, and therefore will get higher search results. In recent years, however, the drastic improvement in search results thanks to a keyword domain has begun to decrease.