This installer is a self executing JAR file. It should start by simply 
double-clicking it. If this doesn't work you can start the installer manually by
typing "java -jar installer.jar" from within the console of your operating system.
Make sure you are in the directory containing the installer JAR file.

For windows users there are executables available to start the installer:

setup32bit.exe - select this one in case you have installed the 32bit version of Java.
setup64bit.exe - select this one in case you have installed the 64bit version of Java.

Now, don't worry if you don't know which version of Java was installed; you can just try and start either of them.

Enjoy!