In a basic approach each container works independently, they don't know from where cards are coming and where they are going. The Board widget allows to link multiple containers together allowing to have seamless transitions when cards move from one to another.
Using the Board widget is very simple, just add it to your scene as you do for any other node. Then you can place as many containers on it as you need as children nodes. That's all you have to do.
Note: at the moment for the Board widget to work properly, containers have to be direct children of the board.
Please check out the demo to see how it works, by pressing the Board Demo button in the main menu or looking at the source code.