You should also avoid words that have more than one spelling if your visitors are likely to be confused and mistype the name. Alternately, you can buy both versions of the name and direct visitors from the one you like less to the preferred name. While you do want a short name (see below), don’t go for something so cryptic that people have a hard time remembering it. Word of mouth is a powerful marketing tool and you want to make it easy for people to tell their friends about your site.
Before you sign up for Web hosting and start building a website, you need to buy the domain name where visitors will find your site. Hundreds of different registrars sell domains, so first and foremost, know that domain names work the same no matter which registrar you use. You don't need to buy your domain from the same company that will host your site. Aside from picking a registrar -- and, of course, your site's name -- you also need to pick a top-level domain like .com or .org.
There are organizations that are called registries that manage each TLD option. When you register domain names, you would first visit a domain registrar who would in turn check with the registry that manages that TLD to see if the domain is available. If the domain for the TLD you want discovers that it is in fact available, the registry adds it to their registry and gives you access to it. If the domain has already been registered by another user for that TLD, you will be shown during the domain registration process that the domain isn't available.
When you buy a Premium Domain name, you are also buying strong branding potential, high recall, and the ability to attract more traffic to your site. Finding a relevant domain name to your business will provide you a storefront online, allowing your customers the most access to your products as possible. Your domain name is an investment that is easy to map back to success, and the perfect available domain name is just around the corner.
If you ever change your web host (the actual physical location of your website files), your domain name goes with you. Your regular visitors or customers who knew your site name as (say) www.thesitewizard.com would not have to be informed about a change of web address (also known as "URL"), since as far as they are concerned, the site is still at the same place. They would simply type your domain name and they'd be transparently brought to your new location.
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.
GoDaddy — This extremely popular registrar (probably the biggest today) offers .com domain names for $9.99 (plus 20 cents) per year (or $6.99 plus 20 cents if you transfer from another registrar). They have a web interface to manage your domains, free web redirection (where people who visit your domain will get transferred to another web address of your choice), free starter web page, free parked page or free "for sale" page, and an optional private domain registration where your domain is registered in the name of a proxy company. Besides .com, they also sell .us, .biz, .info, .net, .org, .ws, .name, .tv, .co.uk, .me.uk and .org.uk, etc. Note that (as with all registrars) the exact price varies depending on which domain you are registering (for example some domain suffixes are more expensive than others). Both credit card and PayPal payments are accepted.