An Applet on that page will automatically test your machine and create a window that it controls in which to run user jobs. These user jobs are written in Java, and executed inside your browser, so your machine is completely safe. Then you can go to a Java Market Web page and tell it who you are, how long you want your job to run, and what the files associated with the job are. It will take it from there, editing and compiling your Java code and then shipping it to a producer machine. File operations will be handled remotely to the Market machine.
Results are returend to the user via e-mail.
If you have a Java-capable browser and the Market is being run, you can play with it now. Please don't do these all from one copy of the browser. Reusing job names can confuse Netscape, even if its cache is set to 0 bytes. It can use any correct Java Applet as the instruction set for the job, and the infrastructure exists for expanding the capabilities of these Applets without compromising security. The Java Market can make use of any machine, with any operating system, as long as it has a Java-capable browser.