A dns server knows what and where things are. That’s its only real job, to tell who’s asking where say, http://eff.org/ is.

“Ay homie, where’s https://eff.org/?”

over here - 173.239.79.200

“thanks, bud!”

The issue is, the dns server you use by default is under the control of whoever your provider is, and as a result, they get all of your dns lookups like the example above as well as every porn site, every piracy site, everywhere.

Installing your own, or simply moving to one your provider has no business with like 9.9.9.9 can help keep your dns queries more private, go a step further and use encrypted dns, as many providers supply, and you’ll be even further covered.

Installing your own, however, comes with the added perk of being able to apply your own dns entries. Suddenly local addresses can have custom names without ever touching a hosts file. Neat! Use DNS certs and you’ve got local SSL!

I would go find something applicable to feed you for a dns 101, but my old resources don’t exist. I just know stuff from years of doing it and failing over and over until things work.