must for obligation,
mustn’t for prohibition,
can/can’t for permission
and should for advice.
Ideally speaking it should be played by four-to-six players, but I can’t see any reason why you can’t ‘play’ on our own. Ok, if you play on your own you will be revising modal verbs, but you might be killing all the fun.
Before you play, you must get familiar with the game by reading the rules. The rules page will give us access to all the other components of the game:
You need a driving licence that you can download if you wish.
You need to get acquainted with the road and traffic vocabulary as well as with the modal verbs. You can do all this from here, with the added bonus that there is and audio file for each of the vocabulary items, which will enable you to get the pronunciation right.
Finally, you are given the solutions to all the questions in the game.