What is a domain name? A domain name is location of your website on Internet. Your domain name will be what you become known by online so it's important to get it right.
Each website on Internet is labelled with something called an IP address which is actual address of website online. A typical IP address looks like this: 22.214.171.124. Remembering a string of numbers like that is difficult so a domain name translates all those numbers into something like www.amazon.com. This is far easier to remember.
#1 Dot what? Each domain has what's called an extension. The most well known of these extensions is .com. This, however, is not only type of domain extension available. There is also:
.net If you can't find your preferred .com domain name you could always choose same domain with a .net extension. It might not have same ring as a .com but is still as just useful as a .com.
.org These domain extensions were orginally designed for educational and more formal websites. Anybody can register a .org however so you have more options for domain selection.
.info A more recent introduction to domain name game are .info domains. Many of valuable .info domains were bought up overnight but there's still a huge range of good .info domains available. With a little creativity you could really make a .info work for you e.g. www.moviereview.info.
Bear in mind that most web surfers tend to remember .com more easily than anything else.
#2 Branding vs Business Name There is an age old debate on whether or not you should establish a brand name online or use a domain that more actually reflects your real business. Let's look at Amazon as an example. Amazon sells books online. Most people setting up a business would have chosen say www.booksonline.com instead of www.amazon.com. Amazon has since established itself as a brand name of global recognition - proving value of building a brand name.
You'll need to choose between two. Brand name or your own business name. Consider how your domain sounds, how it might look on a business card and how well it relates to your business.
There's no one right answer to this question. You need to choose what makes most sense for you, your website and your business in general.
#3 Hyphenated or Not? This is another area of debate. Should your domain be one single word or should words be separated by hyphens? There are advantages and disadvantages to both approaches. Single word domain names can be easier to explain, use on header paper and lend themselves to brand names very well. Single word domains are in very, very short supply.