A handful of domains will have restrictions on them, which means you can only purchase them if you meet certain criteria or have authorization (some examples are .gov, .edu. and .mil). But most extensions are available to everyone. In fact, most country code Top Level Domains (ccTLDs) are available for anyone to purchase, even if you don’t reside in the country in question.
The suffix identifies the name as belonging to a specific top-level domain (TLD). As of late 2016, when this article was written, there are numerous TLDs available for general purchase, including .com, .edu, .game, .green, .hiphop, .net, and .org. The most popular of these by far is .com, which is supposed to indicate commercial sites, but in reality has come to include almost everything.
Hostt is a just-launched free web hosting company that includes domain name purchasing and registration. They've a suite of offerings, such as one where you'll pay $13.99 per year for domain names with extensions that include .com, .net, .org, .us, .biz, and .info., but have unlimited bandwidth, web space, sub-domains, parked domains, sub-domains and email accounts, among other things. Like HostGator, they include domain locking and automatic renewal, along with a user-friendly management portal (which, believe me, is pretty rare) and 24/7 technical support. This isn't a bad price considering the amount you get, and their $3.95 and $5.95 a month packages both offer fairly balanced domain-inclusive packages.
If you get a domain name that describes your company's business or name, people can remember the name easily and can return to your site without having to consult their documents. In fact, if you get a good name that describes your product or service, you might even get people who were trying their luck by typing "www.yourproductname.com" in their browser.