When your computer does a DNS lookup, it will check the "hosts" file for an entry on the domain. As a result, you can point a domain to any IP that you want. For example, when testing a new version of a site on a different platform or server. The hosts file is a plain text file that is edited using a plain text editor such as notepad, textedit, gedit, etc.
Edit the hosts file:
Windows: C:\Windows\System32\drivers\etc\hosts
Linux / Mac: /etc/hosts
Once opened, add an entry similar to:
1.2.3.4 example.com www.example.com
Where 1.2.3.4 is the real IP and example.com is the real domain. It is important to have the www record also unless you exclusively use the non-www version.
Save the file, restart the browser, and the domain should now point to the entered IP and you should see that version of the site.