Hi,
better ask this in the "Beginners" forum: http://community.jboss.org/en/jbossas/beginners
1. "GA" stands for "General availability" and is a release version, which is meant for production usage (no beta or milestone or RC = release candiate).
2. hope this helps: http://docs.jboss.org/jbossas/jboss4guide/r5/
Best regards
Wolfgang