Wikipedia has good articles on FIRST and its programs, with a list of games for each competition:
FIRST
FRC
FTC
FLL
FLL Jr.
As others have said, competitions are the best way to see how it works, especially off seasons. They're usually fairly small and just one day, but still a lot of fun! Have him at least watch the game animation first, and maybe previous years' animations for more info and entertainment. Reading at least some of the manual so he better understands the game and scoring can't hurt, and having him talk to other teams probably isn't a bad idea!
I would definitely recommend Chief Delphi, even he's not sure about some of the stuff, reading the threads and looking at the pictures will help him learn.
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