There's a link on the release notes page that explains the security baseline and its use in detail:
http://java.sun.com/javase/6/webnotes/family-clsid.html
As for the Olson data, it's simply a compilation of information about the world's time zones, like uniform zone names, UTC offsets, DST applicability etc.
Nothing a typical Java developer need be concerned about; that is about the baseline and timezone db versions.
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.