You should be able to see a grid of cells in the section above on this page. If you cannot see it then your web browser may not be able to run Java applets.
With your mouse, activate your chosen cells in the game area. For some example patterns see below.
To start the game slick the 'Start' button. To stop the game, click the 'Stop' button. To run the game a single generation at a time, successively click the 'Single' button. Finally, to clear the game area click the 'Clear' button.
The following zipped file includes the java source code, compiled class file and an example .html file to display the applet in a web page.