You could face the following problem. You could be intending to set up your own Web-server, for it to be visible to the public, on your home computer. You could have an ISP, which assigns and reassigns you IP addresses which they own, and which therefore, you do not own as static IP addresses.
You could have taken the step of installing a Web-server on your machine, as well as to do “Port Forwarding” on your router, meaning that the router listens on Port 80 on the WAN, and forwards all incoming connection attempts to that port, to the host machine on your LAN.
You would now have the problem that your Web-site needs a URL, with a domain name, which anybody on the Internet can use, to access your Web-server. After all, your IP address can change, and it would not be practical to update people directly, with your new IP addresses.
There is a freemium service on the Web, which would be able to help you with that problem. When we give our Web-browsers a URL with a domain-name, the browser accesses a public DNS server, to look up the IP address of the Web-site, associated with that domain name. “DynDNS” offers a specialty service, by which its members have ‘a Dynamic DNS service’. Its members install an update client on their machines, and reserve a domain-name with DynDNS, which is to be associated with their potentially changing IP address, continually.
Whenever the ISP changes our IP address, the update client on our computers detects this, and logs in to the DynDNS account we have. Then, the update client notifies DynDNS of the new IP address, and DynDNS has the connections with the public network of DNS servers, to propagate the new IP address. It is the responsibility of DynDNS, that requests for domain-names which its members hold, from Web-browsers, be answered with your updated IP address.
The Web-browser is never notified in any way that your IP address or domain name are different from ones with static IP addresses, it simply receives the IP address from its subscribed DNS server, that is your WAN address, and connects to it.
Further, if you have registered a host-name, as they call it, with DynDNS, there is no specific reason why you would need to listen on Port 80 always. Your purpose could be to make other services publicly-accessible, which listen on other port numbers, which you have instructed your router to forward to some machine on your LAN.
This is the arrangement by which I host my own Web-site, and additional services, from my home computer.
dirk@Phoenix:~$ host dirkmittler.homeip.net
dirkmittler.homeip.net has address 220.127.116.11
dirkmittler.homeip.net has IPv6 address 2001:0:53aa:64c:d1:32e7:b9cc:d8a8
dirkmittler.homeip.net mail is handled by 10 plsmtp1.hushmail.com.