Those trading domains for commercial purposes are generally on the prowl for lucrative domain endings. There are essentially two different ways traders go about making money off of domain names. One method entails purchasing already established names for a low price and selling them for a profit later once their value has increased. Another strategy involves buying and registering a domain that is thought to possess a high sales potential. Many domain traders use backorder services. These services automatically register a domain when one becomes available or is deleted (what are known as expired domains).

Name servers. Most registrars provide two or more name servers as part of the registration service. However, a registrant may specify its own authoritative name servers to host a domain's resource records. The registrar's policies govern the number of servers and the type of server information required. Some providers require a hostname and the corresponding IP address or just the hostname, which must be resolvable either in the new domain, or exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required.

The way that competition is supposed to work between registries, is that lots of companies go to ICANN and say “We think we can reliably manage .com, and we think it would cost us [$5] per domain.” ICANN reviews these bids and awards the .com contract, which lasts for a fixed period of time, to whomever they deem best-suited to the job. In this time, other companies can think of ways to manage .com better/cheaper, and try and win the next contract. This, in theory, would provide an incentive for registries to innovate, a big part of which would be in lowering costs.
If you're having trouble finding a domain name (whether because of crowding or cyber-squatters), check for a help facility on each registrar's site. Domain registrars typically house search engines that return a listing of available names similar to the one you want. When you search for a domain name at Namecheap, for example, you get both the status of that name and a list of suffixes available for that name. Maybe [Sitename].com isn't available, but [Sitename].biz or .org is.
DNS is essentially a database of IP addresses.  Each IP address is a series of numbers that allow computers to communicate with each other. A website is identified on a server by its IP address. Instead of your visitors having to remember an IP address to type into their browser to access your site, they instead use your domain name. When your domain is entered into their browser, DNS translates it into an IP address because that is what computers understand.Your computer is able to connect to your web hosting and show your website on the browser once the IP address is found.

A great domain name is a concise, easy to type, and memorable URL that reflects your brand or your website’s subject matter. Avoid using hyphens, strings of numbers, or unnecessary words to make it easy for your visitors to remember and find your website. Remember: A great domain name is one that your visitors can type correctly on their first try.