A domain name consists of one or more labels, each of which is formed from the set of ASCII letters, digits, and hyphens (a-z, A-Z, 0-9, -), but not starting or ending with a hyphen. The labels are case-insensitive; for example, 'label' is equivalent to 'Label' or 'LABEL'. In the textual representation of a domain name, the labels are separated by a full stop (period).
Most people assume a domain name ends in .com so if you buy a domain name with one of the other extensions (.net, .info, .org, etc.), you’ll have some extra work to get people to remember that your site has a different extension. Don’t automatically assume you should only buy domains with .com, though. Many sites have done quite well with other extensions. (Look at us!)
More controversially, the new agreement guaranteed the renewal of Verisign’s contract in 2012 unless they were in “fundamental breach” of their obligations as a registry. A similar presumptive renewal clause in the 2012 agreement recently sealed Verisign’s control over .com until 2024. This kind of arrangement, ICANN say, incentivises registries to make long-term investments in infrastructure that benefit the Internet community.

A few companies have offered low-cost, below-cost or even free domain registration with a variety of models adopted to recoup the costs to the provider. These usually require that domains be hosted on their website within a framework or portal that includes advertising wrapped around the domain holder's content, revenue from which allows the provider to recoup the costs. Domain registrations were free of charge when the DNS was new. A domain holder may provide infinite number of subdomains in their domain. For example, the owner of example.org could provide subdomains such as foo.example.org and foo.bar.example.org to interested parties.
When you type google.com into your browser, the domain is split into parts by the “dot”, from right to left. The first part is “com”, so your computer checks the root zone file to see which registry manages the .com TLD. It then checks with this registry to see where the next part, “google”, points to. The registry returns the IP address, and your computer can then ask Google to send their homepage over.
In the first quarter of 2015, 294 million domain names had been registered.[17] A large fraction of them are in the com TLD, which as of December 21, 2014, had 115.6 million domain names,[18] including 11.9 million online business and e-commerce sites, 4.3 million entertainment sites, 3.1 million finance related sites, and 1.8 million sports sites.[19] As of July 2012 the com TLD had more registrations than all of the ccTLDs combined.[20]
My personal preference is to register the name directly with a domain name registrar rather than through my web host. I've heard stories, in the past, of less-than-reputable web hosts that registered the domain under their own name, making them the owner of the domain rather than you (although I don't know if such web hosts still exist today). Registering direct with a domain name registrar allows me to make sure that I am registered as the owner, the administrative and technical contacts. Being the owner is vital — if someone else places himself as the owner (such as your web host), he can always decide to charge you some exorbitant fee for the use of the name later, and there is little you can do. The various other contacts are less vital, but may still play important roles, depending on your registrar. For example, for some registrars, the administrative contact's approval is required before a domain name is transferred out of a web host (or at least, it used to be). If he/she cannot be contacted, the technical contact is used.
In order to register any domain, you must provide certain personal information that you may not wish to be publically searchable in the Whois database. Signing up for WhoisGuard is a great way to keep your registration data private. WhoisGuard acts as a "shield" for your searchable information, displaying the address, phone number, and email of the domain registrar (Namecheap, e.g.) instead of your own. Keep in mind that WhoisGuard is an optional security add-on that must be renewed separately when you renew your domain.