Domain name service works thanks to DNS servers. It is these vital "programs" that store the "domain name" - "IP address" correspondence tables.
In addition, DNS-servers serve to store resource records of domains.
There are a huge number of DNS servers on the Internet and each performs its own function in the overall system. Domain Name System service is necessary so that we can easily find our favorite sites without having to remember strings of numbers.
I think the dude is more interested in applying this thing to specific problems. For example, as in the article: https://technologeek.net/free-netflix-dns-codes-for-us-2021/
Personally, I've encountered it more than once. I love their series.