When you use this feature, you can choose an AI difficulty stage where you can play the game just around a level when you can beat the AI but not to full strength. In this way, you can see the bad moves that are keeping you from beating the next level.
The Play vs AI feature is available for both Chess Roll (dice chess) and Chess games. For Chess Roll, you can access this feature in the Home Lobby page. Just click the second big photo in the center which says Play vs AI. Once you click this, you will be given the option to choose from the three AI difficulty levels available: Easy, Medium, and Hard.