If you click on "start program" there should open a new tab in your browser with a "New graph" button in the center.
If this does not happen, then maybe
- your java plugin is too old,
- you did not allow the applet to start, or
- your browser blocked the java plugin.
- you have to add this website (http://www.free-graph-theory-software.org) as an exception in the security settings of your java control panel.
- you should visit the website use-java-plugin-to-view-interactive-content.