The Dual N-Back game field is a square separated to smaller squares with lines (like 3x3 cross-zero game field). During the game the image is show in one of the game squares. Your task is to find a match between the current position of the image to the position shown one (or two) step earlier. And if there was a match press the corresponding match key. The same is with the auditory letters. Just listen and try to remember the letters from the previous steps.
Unlike many other brain training exercises Dual N-Back is proven to transfer training results to other brain activities. This effect has been confirmed by a number of scientific studies.