If you want to contribute code (p.e. a bugfix), a test or documentation (p.e. an additional example), please do the following:
1) Make sure your code doesn't break the existing one and that Fop still compiles.
2) Create a file which shows the differences to the existing code.
One of the committers will test your code and commit it to the code repository.
If you have a test or useful bug test you should read this page.
BTW: The Apache project knows different roles for contributors, namely 'users', 'developers', 'committers' and the 'Project