How to buy a domain name?

[Sanders]

How do you actually buy a domain, not rent one annually?

[vicecaptain]

You can't buy a domain name for yourself. All the domain names must have to be registered for a certain period of time only (Maximum 10 years). even famous domain names like google.com, facebook.com are also registered domain names for fixed period of time. But you can keep renewing your registration period for any much of time.
You can register your domain name from any of the domain registrar. There are many sources for it. If our desired domain name has already been registered, You can have Whois lookup on the specific domain name. This would give the domain registrant information through which you can contact the domain holder for a bargain if he or she wishes to sell it for you. You can have a whois lookup for a domain name from www.WhoisXY.com All the best mate.