You don't need to download the FOP software, our .war file includes the required jar files.
For a short inroduction what fop is you can refer to http://xml.apache.org/fop/index.html#intro. To download the software follow
this
After downloading you can see the HTML-Documentation in the subdirectory <installdir>xml-fop/docs/html-docs.
For developers read the readme file that comes along with FOP. Check the compile job compile.cmd to put your classpath correct.