The API (Application Program Interface) allows you to control your panoramas and virtual tours from outside the viewer applet. For example, you can offer the user viewer controls when presenting panoramas without a skin. Users can control the panoramas by clicking on text links, images or HTML form elements such as a buttons or drop-down lists. If you are familiar with image mapping, you can map an image - floor plan or arial photograph - linking different part of the image to different panoramas in your tour. The API also allows you to create you own 'controls skin', remote and completely separate from the viewer skin.
The parameters set in the applet code are static values - they are applied when the applet is first loaded. Their functions are to instruct the applet to do this¡when it first loads. For example, the parameters tell the browser which panorama to load and where to find it, what the frame rate should be, whether to pan left or right, etc. The API, on the other hand, allows you to override these parameters. It offers you and the user dynamic values that can be changed from within a web page.