Take this file and copy what you see on the screen into a file WelcomeApplet.html.
Then copy the other file (in the same folder) as WelcomeApplet.java.
Compile and run this file, the run appletviewer on the HTML file.
Read more about the aplplet by clicking the link next to the source code file.
Note: although using an appletviewer is in general OK, it won't work here.
The reason: the appletviewer can only load applets, can't do any of the other browser things.
So, load it in a regular browser instead, e.g., Firefox etc. (because you need browser functionality).