DNS stands for Domain Name System, it resolves URLs to IPs, which are the real addresses of websites.
How Secure DNS works?
Secure DNS operates by filtering out known ads, tracking or threats URLs before a query is sent to a trustworthy upstream DNS server.(such as Google and Cloudflare)
How to use it?
Use the Secure DNS IP or address as the only DNS server in the network settings of your router or device. more detail steps could be found on the internet for your sepcific router or device.