If you've been following my Amber by the Cards design, you'll know that at the end of character creation, the players will have jokers that they haven't used yet.

You don't need to be following AbtC to follow this mechanic.

This mechanic is intended to foster conflicts between PC's, and to give people goals to strive for, to create a tapestry of conflict in which the players can define their characters.

Here's what they're for:

The players take turns, stating a scene that they want to see happen in the game.  They can name PC's or not.  Ideally, they should be fairly general in nature.

"Someone discovers a fourth pattern, associated with the sun rather than the moon."

"Deirdre and Corwin get married."  (Yeah, I know.)

"Blackburn emerges from the ruins of Garnath sworn to vengeance."

"One of the towers of Castle Amber collapses."

"One of us invades Rebma."

"A new king is crowned in Amber."

After stating the scene, the other players have an opportunity to second the scene.  A player seconds the scene by paying a joker to the game moderator (AKA "The Pattern").  The Pattern writes down the cool scene on a 3x5 card and paperclips the joker to it.  It is now a "Pivotal Scene"

Players may also veto a scene.  This is also done by paying a joker to the Pattern; the scene is removed, any jokers clipped to it are returned to their owners, and the player who suggested it goes to the end of the line.  The joker that was handed to the Pattern is added to the Pattern's pool of free jokers.  (free jokers are used elsewhere).

If the scene isn't seconded, then the player goes to the back of the line for another chance.

After everyone has had one scene seconded, then the Pattern reads off all the pivotal scenes, and the players vote for them with their remaining jokers (average one per player).  To vote for a scene, a player pays a joker to the Pattern, who clips it to the scene that received the vote.

Once all votes are cast, the Pattern ranks the scenes in order of number of votes.

Seconding or voting for a Pivotal Scene is a statement; "I care about what happens in that scene."

<<there's another few steps in here which I am skipping>>

Once play has started, if the event described in one of the Cool Scenes comes up as the subject of (or part of) a conflict between PC's, then the winner of that conflict is awarded the joker(s) that are clipped to that cool scene... but only if there are no other cool scenes that have FEWER jokers clipped to them.

This means that all the pivotal scenes with one joker must be played before all the pivotal scenes with two jokers; all the pivotal scenes with three jokers must be awarded before the pivotal scenes with four jokers can be awarded.

You can play a to a pivotal scene before its time comes... for example, if "One of us invades Rebma" has four jokers, that doesn't mean you can't invade Rebma before the lesser-ranked scenes are awarded; it just means that you won't get the award for it.  You'll have to invade AGAIN after it becomes eligible.

It's the Pattern's job to keep people aware of the scene level, and what has been awarded.

Jokers that are awarded by this mechanic become part of the character advancement mechanic.  This is not the only way to receive jokers.