When you start the app you will see the above screen. If you want to generate a board then press either the 3 cube or 4 cube icon to get a random board formed with the respective number of cubes.

To work on a real live board you can press the camera icon to take a picture of the board. If space is limited on your device, you can doubleclick the blank area to hide/reveal the 'Cubes Left' buttons.