Thank you a lot for your feedback and for playing the game! Yes we got quite a few complaints about the UI being unclear ahah
So, basically, it is an orthogonal representation of the die:
The face in the center is the one on top, the ones on each of its sides are the adjacent faces, the one on the bottom is on the other side of the die.
This means that when you move up, for example, the face that was previously "down" compared to the central one would roll in its place.
It's really unintuitive as it is, we would have liked to have more time to experiment with other UIs or to add animations