Domain names disappear extremely fast. Many people claim that all the good domain names are gone. I doubt that — but it is probably true that most good domain names that are descriptive of products and services have been taken. If you want a domain name for your site, I suggest you act now, or face the anguish of having lost that name later. After all, US$10 (more or less) for a year's ownership of the name is rather cheap when you realise that you're securing a good name for your website.
Many registrars reserve the right to revoke your domain name for specific reasons, typically if you use the domain for illegal purposes or purposes deemed unacceptable (such as spamming). Many contracts contain a clause letting the registrar delete your domain name for no apparent reason. The implication, of course, is that the domain name is the registrar's, not yours.
Domain name registrations are priced on a subscription-like model that allows a person or business to register that domain name for a certain period of time (usually in annual increments). At the end of the registration period, you (the domain name registrant) have the option to renew the domain name registration for an additional period of time, or let it expire. It is important to renew your domain name registration, or you may find that all of your work building traffic and views to your site ends up benefiting someone else (in the instance that someone else registers your domain name after you let your registration expire), and potentially costing you more in rebranding.
Registering a domain name lets you create a personal presence on the web. With your own web address, you can control your online identity by linking to any other site with more information about you. For example, you can register a domain name and forward it to a website, blog, or social profile page like your Facebook, LinkedIn, or Twitter pages. A domain name can protect your personal brand and help your career.
If you’re still with me then you might be wondering who came up with all of this. The answer is ICANN — the Internet Corporation for Assigned Names and Numbers. ICANN is a non-profit whose role is to coordinate all the names and numbers that keep the Internet online. They outsource a lot of the heavy domain name lifting to registries like Verisign, who pay ICANN for the privilege.
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.