Thanks for the feedback! I definitely agree that clear instructions would improve the game, the prompt kind of disallowed that exact thing though. So after voting maybe we'll add it in?
In the meantime we set it up so that the player could do literally nothing for the first two rounds and not take any damage. and hopefully they'll see the towers automatically fighting enemies and immediately realize "this is a tower defense game". And I trust that by round three they'll have thought to press at least one of the few lit buttons on screen, if not just to see what they do.