A domain name is the unique human-friendly identifier of a particular website IP address. Anybody can register domain names using service providers known as domain registrars, which keep a registry of who owns a particular domain name. If you need to find out who owns a particular domain name, maybe because you are interested on purchasing it or want to report something happening on their website, you will need to query the public domain registers.
Using a DNS look up service
The registry of domain name owners can be accessed using what is known as a DNS look up service. Most domain registrars will offer this kind of services, because it helps their users find out if a domain is available or not. Alternatively, you can go to Whois.net or Whois.domaintools.com and use the WHOIS lookup feature to check the domain name you are interested in.
Most registrars will show you information such as the registrant's name and company name, address and when the domain will be available. It is also possible to find out the technical contact, in case you want to report a problem with a website.
Accuracy of the information There's no guarantee that the information given by a WHOIS service is actually true, accurate or current, since people may register a domain using a fake name, or change their address before renewal. While domain registrars demand that the information entered is accurate, few or none actually verify it.
Ways to hide the registration data
Most domain registers offer a paid service where they use their own data to register your domains, effectively hiding your name from a DNS search. However, you can still find the domain owner by asking them.
If you want to report something illegal
If you see a problem with a website or receive spam email from a domain, you can report them to the domain owner registered when you look up the domain. If they are a legitimate domain registrar, they'll take measures and will pass the information to law enforcement, but they won't probably release it for your personal use. If you want to buy a domain
Most of the time the email contact address you can find on a domain look up is not actually working, as people don't like their personal email addresses available for spammers to harvest. However, you can send them a mail through their website, or try an address such as Hello@domainname.com or Admin@domainname.com and see if they answer.