most connections to the internet are through a dynamic external IP address which changes quite often (weekly or even daily).
this can make it very difficult to connect to home services from an external computer.

to get around this, Sy DNS is a provider of what is known as a DDNS (Dynamic DNS) service
we provide a public DNS server that anyone can get a subdomain and use one of our provided scripts to update their record(s).
so instead of trying to remember an IP address, you can use a domain name that is kept up-to-date by a computer at home

once this is done, periodically (usually every 5 minutes), the computer running the client, tells our central system (via a HTTPS post), to update the record with its latest external IP

it's up to you what you do with it, usually the IP address is for your router, most people login to their router and configure certain ports to be forwarded to other computers running that are connected to the router

if you had setup your domain to be exampledomain, then told your router to forward the port 80 traffic to a server plugged into it running a webserver, then from anywhere around the world you could hit exampledomain.Sydns.live in a web browser.

if you had setup port 22 to be forwarded to a raspberrypi running ssh, you could ssh to it with

ssh pi@exampledomain.Sydns.live

A good site to find out how to port forward on your home router is portforward.com