This is a distributed system that keeps track of which domains are associated with which IP addresses.
When a visitor types your domain name into their browser, the DNS looks up the related IP address and leads them to the correct page. In this sense, the DNS can be thought of as an internet directory.
You may need to engage directly with the DNS in a variety of situations, such as debugging issues or setting up a custom email address. It's also crucial when switching to a new domain or hosting company.