Take a quick look at what optimal moves are and how they useful.

There is a feature that allows to see optimal moves with special move mark (green star by default). In order to use it, you have to enable this option in game preferences. When enabled, it allows to see hints from computer assistant on possible moves of selected piece. This is the same algorithm used for playing with computer opponent. That is, it takes into account covered friend pieces, escaping from attacked position, etc. This is good thing for learning but don't rely on this hint all the time, every chess robo is somewhat limited in compare to a human. InCube Chess is a game for humans.

In order to enable optimal moves, you need to do the following:

1. Choose "InCube Chess" > "Preferences"
2. Choose "Battlefield" tab
3. Turn on "Suggest moves" checkbox.