Simply speaking, a domain name is a website address. For example, “city4u.com” is the address of the City For You, which is also the site’s domain name. In this example, http//www.city4u.com, i.e. the complete web address, is called the URL or Uniform Resource Locator.
A domain name has three levels. The first one is the “extension” part of the name, i.e. “.com.” The “extension” is known as the “top level domain” (TLD), comprised of generic (.com, .org etc.), country code (“.us”, “.uk” etc.) and infrastructure domains. The second level is “city4u.com.” while the third is “http://www.city4u.com.”
Before looking for your domain name, you should consider these factors. First, try to use your site’s name as the basis of your domain name as far as possible. If the URL contains your name, customers will easily find you. It is very tough to register a generic domain like biscuits.com as most of them have already gone. Equally difficult is getting ranked in the search engines. Better choose a domain like creambiscuits.com to reduce competition. It may be comparatively easier to register hyphenated names but the hyphens may be forgotten as well.
In case you find the .com or .co.in extension not available, consider instead the .net or .biz. If your domain name is already registered, contact the owner and ask if they’ll sell. In most cases a domain name will be free in the plural but not in the singular form. Although a short domain name is easy to remember, it is less likely to be available. A longer domain, however, can contain more keywords that are useful. If you find your preferred domain name not available, you can always try a prefix or a suffix.
You can find basic information about TLDs at ICANN’s Introduction to Top Level Domains, and information about country code TLDs from Root-Zone Whois Index. However, as there is no single database that lists the owners of all domain names, you will have to search a number of databases.