windowscentral[.]com/how-configure-cloudflare-dns-1111-service-windows-10-and-router
This is a really worthwhile thing to do, though there are a few other DNS servers you can use if you want, e.g., Google's. A DNS server translates the plain language web address you type into your browser into the number-based address that results in the page you want opening in the browser. You want the DNS server you use to be fast, obviously, but you also want it to be secure -- cyber criminals hack into DNS servers to alter their records, so when you type in giveawayoftheday for example, you go to a site that they control that distributes malware. Your ISP most likely has their own DNS server, but they also most likely don't have the resources of one of these giant companies to keep the server(s) fast, updated, & secure.