How DNS turns a name into an address
You type a name, the device asks someone where that name lives, gets a number back, and only then opens the page. That question has a name, an owner and an address — which is exactly why it is the best place to turn off what you do not want.
The query that comes before everything
When the browser shows the address you typed, it still does not know where to go. It asks the resolver configured on the device, a service able to answer with the matching IP number. The answer usually comes back in milliseconds from a cache, but the origin is always the same: a name server.
The one answering that question is normally your internet provider or the router at home. That means this intermediary sees every name you look up, even the ones you type without ever opening the page. The order of the address in the path is precisely what gives DNS its power over what reaches you.
Why turning things off here works better
An ad blocked in the browser has already spent data and has already been requested from the advertiser's server. An ad blocked at DNS level never reaches that server: the query does not come back with the advertiser's address, and the request to it simply never happens. The same goes for trackers that exist only to mark the visit.
And the block reaches everything that uses the device's resolver, with no extension, no per-site configuration and no app to install. A phone, a tablet and the television start obeying the same rule, because the decision happens before any content arrives.
What DNS does not solve
DNS acts on the name, not on the content. An ad served from the same address as the site you are reading passes through untouched, because the name being queried is legitimate. The same goes for tracking by IP address or by browser fingerprint, which stays possible even with a filtered DNS.
DNS also does not protect the content in transit. That remains the job of encryption between the browser and the site, and of a well-configured intermediary. Treating DNS as its own layer, rather than as a replacement for the others, avoids promises the technology cannot keep.