What you are looking for is How to Deploy a Java Applet. Here is a nice tutorial.
http://docs.oracle.com/javase/tutorial/deployment/applet/index.html
If you want your applet to be available from anywhere, you will have to embed it on a page that is hosted on the Internet. Getting a page hosted costs money, especially if you don't host it yourself, but there are thousands of well-known companies that provide this service. I can't provide any advice on which one is best, for fear of being swallowed alive by StackOverflow.
Once you have a page hosted, you can embed your Java Applet by following this tutorial.