If you allow external access to your server, a user can access your computer at port 8080, using your URL (or IP), while the server is running.
If you don't have a static IP, of course that makes it more difficult, since your address can change. There are services that can be purchased that allow a user to access one if their static addresses, and then reroutes to you. Search for them on Google.
You shouldn't need to make any change if it's working now with localhost and you are allowing external users to access the server. They would access using "http://www.sda.com:8080/". You have to specify the port since it's not listening on the http/html default (80).
If you have problems, then the server is probably misconfigured. Refer to server documentation for information on how to use it. You might also use Google to search for "server tutorial".
Your computer recognizes "localhost" as a term (a URL) that points to an IP number, "127.0.0.1" These are only valid in the local machine.
The same 2 things, IP and URL, identify your machine to other machines and the Internet, but they have different values. These values are usually assigned by the Internet provider you use. They are the values that are used by someone wanting to send information to you.
For you (at your machine) to access the server that's running on the same machine, you use localhost or 127.0.0.1
For someone at another machine to access the server that's running on your machine, they needs to use the URL or IP that identifies your machine to the Internet.