Left-click on the applet to zoom in on the point at which you clicked by a factor of 3, and right-click to zoom out. Scroll your mouse wheel up/down to zoom in/out, without re-centreing the image, by a factor of 8. The status bar at the bottom shows:
Various attributes of the applet can be modified by using <PARAM> elements within the <APPLET> tag in the source html (look at this page's source for an example). They are all double-precision (64 bit) floating point values (e.g. 3.1415926535897). Note that if you set X and Y to the same value the status bar will dissapear, which is useful for taking screenshots of the applet window to produce pictures.
Feel free to use the following examples (which use the executable java archive Mandelbrot.jar (15 KB)) or the source code Mandelbrot.java (19 KB), as long as you acknowledge me. I have set up the examples so that they are already centred on an interseting area; so scroll up to zoom into the never ending (until the precision runs out!) depths of the Mandelbrot Set.
This applet is written in Java which is a cross-platform programming language. To achieve this high level of portability it is an interpreted language, running inside a virtual machine (VM). You therefore need the Java Runtime Environment (JRE) to run Java programs. This applet is written using Java version 1.5 which is also confusingly called version 5.0! You can download the required files from http://java.sun.com/j2se/1.5.0/download.jsp. Click on the bit called JRE 5.0 Update 4 (it might change in the future). You don't need the JDK or NetBeans, these are for developing Java applications.