What is the Dynamic DNS function in cPanel, and what can I do with it?
Generally speaking, Dynamic DNS is a service that keeps track of the appropriate IP address for a given service, then updates DNS for its domain/hostname dynamically to reflect the new IP when it changes. Most typically used to access things on a home or office network served over a dynamic IP when a static IP is not available from one's ISP.
In the context of the Dynamic DNS page in cPanel, this is a tool that allows domain administrators to leverage DNS nameservers controlled by their cPanel server to host domains/hostnames in a manner that automatically updates when/if the IP address it should point to, changes.
This feature works by generating a URL(hosted on the cPanel server) to which a service or device will connect and update DNS automatically. Once the URL is generated in cPanel, it will need to be configured within the service or device on the external network to connect out periodically to that URL. Most likely a router, but could be a dedicated application hosted there, depending on the environment. The device will have to connect out to the URL, where cPanel will then accept and process the request to update DNS for the specified domain, pointing to the IP address from which the request was received.