The internet was once described by Sen. Ted Stevens (R-AK) as a "series of tubes" in 2006. While he was heavily panned for that remark, it was actually a simplification. The internet runs generally like an old-fashioned pneumatic tube system, with each domain getting an address unique to it that is registered under the Domain Name System (DNS).
DNS is the phone book of the internet. Your computer won't automatically know what address you are typing in. It needs a multidigit number such as 184.108.40.206 to tell it to go to google.com. That number is called an "Internet Protocol" (IP) Address. There are two types of IP addresses: IPv4 which has been the standard for decades, and IPv6 which uses hexadecimal characters and came about because we were running out of IPv4 addresses.
The problem with the Domain Name System is that all traffic sent over it is in plaintext. That means that anyone using the free WiFi in a coffee shop is susceptible to a "man in the middle" (MitM) attack, where someone else with a hotspot and some fancy equipment can just read what you're doing over the internet in real time and thus possibly just grab any password you enter. This is where two things come in handy: A DNS resolver and a VPN, but I'm only going over DNS in this article. VPNs will have their separate entry because that's a whole other rant.
A DNS resolver routes the traffic itself through a protected address but not the metadata (I go over the gist of metadata in Messengers). Even Google runs a halfway decent DNS resolver. If you want to go on easy mode, I recommend either Quad9 or AdGuard DNS. If you want to actually block trackers from getting in on your DNS traffic and you know what you're doing, NextDNS is right for you.
You can change your DNS in nearly every major operating system. There are instructions for Windows, Linux, MacOS, and Android. Most DNS resolvers have a downloadable file to where you can install the DNS profile on iOS (Cloudflare makes you use their app, which takes up the VPN slot and is thus not recommended). I personally use NextDNS and block tracker URLs that are picked up using an Android app called Exodus. If an app has specific trackers on Android, it's a safe bet that the same app on iOS has those same trackers (the whole "ask app not to track" thing on iOS is respected as well as the "Do not track" feature in every major browser; that is, not at all).
Now you know a little about how the internet works and a little more on how to defend yourself against the surveillance industry.
TL;DR version: Use Quad9 or AdGuard DNS if you want easy mode; use NextDNS if you want to fine tune everything.