Doubling Cube
In match play, games start off as worth one point. Before rolling, the active player may decide to double the stakes by offering the doubling cube to the other player. If that player accepts the cube, the current game is worth two points. If the player passes, it ends the game and the player who offered the double gets the current stakes. (That's one point if the stakes haven't been doubled.)
If the double is accepted, the cube goes into the possession of the player who accepted it. The game continues as normal with the active player rolling. Only the player holding the cube can redouble, which passes the doubling cube back to the other player.
Doubling should only be offered when the active player has a clear advantage. If the advantage is overwhelming, the other player should usually decline. That's because it's better to lose one point now than risk losing two points later. If the advantage is minimal, accepting the doubling cube could be the right move.
Doubling cube strategy can get quite complicated, but generally offer when you think it will be a difficult decision for the other player.