Every computer connected to the Internet has a unique IP address assigned to it. No two computers connected to the Internet at the same time can have the same IP address. Usually you will get a different IP address each time you connect to the Internet, or, if you have high speed Internet, your IP address may change every few days. This is called Dynamic IP addressing. Your IP address is a little like your phone number except it can change every day or two. Imagine what the phone system would be like if everybody's phone number was different each time you tried to call someone.
This is your current IP address. (18.104.22.168) If you come back to this page in a few days you will notice the number will probably be different.
If you want to host a web site, an Internet radio station or your webcam on a computer in your home, chances are you would want a domain name so that friends and family could use "yourdomain.com" to reach you. But this usually isn't possible simply because a domain name must point to a static IP address, (one that never changes) and there's a good chance that yours changes every day or two if not more often.
What you need is for your domain name to be able to keep track of your changing IP address, so that other users on the Internet can easily reach you.
Dynamic DNS service
A dynamic DNS service is the solution to this problem. These services allow you to associate a friendly, easy-to-remember domain name with an Internet-connected computer, even if its Internet connection uses dynamic IP address assignment.
The Dynamic DNS service software is installed on the computer where you want to host your webcam or Internet radio station. The software keeps track of your computer's current IP address, and it automatically notifies your dynamic DNS service whenever that IP address changes. The service then modifies the DNS zone records associated with your domain, and the change takes effect almost immediately. The bottom line is that anyone typing your domain name into a web browser or other client software will be led to your current IP address. No matter how often it changes.
Many dynamic DNS services offer a free level of service for home users. This level usually allows you to pick a subdomain off one of their domains, like jonny.dns2go.com or cowboyfrank.dns2go.com
Then there are extra services and fancier packages which cost something. I use a pay service called DNS2go.com which allows me to use a full domain name like CowboyFrank.com rather than a subdomain off their domain. You can search the Internet for Dynamic DNS service and you will find quite a few. Do a bit of research and try one out.
One fairly extensive list of Dynamic DNS services can be found at http://dnslookup.me/dynamic-dns/. Don't assume the prices on this site are current, like me, he doesn't have a lot of time to keep lists up to date. You must check out the individual services for pricing and packages.