Beginning in mailing list is always frenetic, community has always something to say to us, and one of our committers was kind enough to create a video and published on youtube to teach you how to submit patches to the Apache Flex project.
If you're still wondering out to create patches and submitting them, watch how Nicholas made it.
Video shows you on IntelliJ IDE, but applies on any other IDE you might have, same work behavior.
Compiling and Contributing to Apache Flex
Nicholas, kudos to you!