DNS (Domain Name System) is like a phonebook for the internet that translates human-readable domain names (like www.example.com) into machine-readable IP addresses (like 192.0.2.1).
Changing the DNS of a domain means updating the settings that control which server is responsible for handling requests to that domain. You might need to do this when you move your website to a new web host or domain registrar, or if you make changes to your web server settings.
It's important to do this correctly to ensure that people can find your website and that it works properly.