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.
SnapNames is a web domain name marketplace - meaning that they only deal specifically with domains that are currently owned by somebody else. They offer daily and premium auctions, private brokerage of domains, and buy-it-now listings for buying and selling domain names, including over 30 million domain names that aren't all, as you'll find on some services, exorbitant. They have over three million customers, including a significant number of small businesses, which is worth it.
I was preoccupied with Hurricane Michael last week (thankfully no damage in our part of Florida) so I have two weeks worth of sales data for you this time around the track. It was a great fortnight for country code domains. The ccTLDs took the top spot on our latest all extension Top 20 Sales Chart, three of the first five and a half dozen entries overall. Casino.ro led the way with a blockbuster $255,200 sale at Sedo. That almost doubled the price paid for the previous 2018 ccTLD leader ($138,040 for Bad. de last month - also via Sedo).
Domain names can be used in a number of ways. Direct visitors to your website’s home page or use complementary domains to send them to specific areas of your website ( e.g. yourcompany.jobs for a careers page). Or, forward a custom domain to an existing social media account, like your Twitter profile or Periscope channel. With a domain name you can even set up custom email addresses like firstname.lastname@example.org, which can be used to conduct business or communicate with your followers. More.