The scrollable box at the top of the applet is for output, and at the bottom of the applet is a one-line text input box. You can also get debugging output on the Java console of your web browser.
There is an animated version of this applet that uses SVG graphics.
The applet runs the PMM, and prints the tasks required as it goes. You will also be asked questions about selecting tasks from a list (selection), whether to continue loops (repetition), and how many instances of parallel tasks to create.
Normally, the applet will output the project instance when the PMM has finished running. However, if you enter "q" when you are prompted for input, you can make the PMM stop half-way through and output a half done project, which can be picked up again by the applet (as long as you use the same PMM, of course) and continued on with. Try entering halfdoneXP.xml to try this out. Note that, since the PMM is embedded in the Project instance, you don't need to re-enter it.