Rose: It's quite simple. The object is to get to some number of points, for example 9.

Games are worth 1 point each to start with.

If you get doubled and accept, the game is worth 2 points, meaning whoever wins gets 2 points.

If you reject the double your opponent will win the game but get only 1 point.

Once you accept the double, ONLY YOU can double again. In this example you would be doubling the game value to 4, and if your opponent rejects you would win the game and get 2 points.