You can read this blog entry, and this
-- F.A.Q. --, but it basically is normal PFS with the restriction that players can only use five sources:
•
the Core Rulebook (that all should own)
• the Character Traits Web Enhancement,
downloadable here (below Free Pathfinder Roleplaying Game PDFs, on the left)
• the current
Pathfinder Society Roleplaying Guild Guide
• the
Faction Journal Cards
• and the boons and items listed on your Chronicle sheets
(you'll never read them the same!)
PFS CORE CAMPAIGN is mainly about simpler characters, which raises the challenge level, while making it a good entry for new players (and allowing veterans to replay completed scenarios).
Remember to select PFC when you create your character on Paizo ; and to not play your CORE character in Standard games, or vice versa.
CORE gaming is... fun!