Each class deck will contain 4 characters, with two roles each, and rules card, as well as 97 boons from all the types of boons the 4 characters might want in their deck. As for which particular cards it will be, that hasn't been said. Though it has been said some will be from RotR, some will be from S&S, and some will be new.
As for how exactly they will work in organized play. It will go like this:
1. You'll choose a character and construct a deck from the boons in that character's class deck with the Basic trait.
2. You'll take you character and his deck (along with all the other boons you didn't put in the character deck) to an organized play location.
3. You'll play there with other players (someone will have to supply the Skull and Shackles base set). The locations will be built from cards in the S&S base set. You'll acquire those cards while you play.
4. At the end, when it is time to rebuild your character deck, you'll trade in a card from Skull and Shackles for the same type of card and adventure deck number from you class deck boon. So if you acquired this Dagger Pistol +1
, you would trade it back for another Weapon of Adventure Deck 2. Then rebuild your character as normal.