I knew this would be a problem so I added a "How to play" function in the menu but unfortunately I can't release it until the jam is over :/
The game has three main inputs, the mouse click, "M", and "A". The mouse click chooses a place to either move or attack, in the Move phase you confirm your move choice with "M" and then that advances the game to the Attack phase where you can pick an attack location and confirm that choice with "A". The execution phase then begins (no inputs there) and once that's done it's back to the move phase.
You're completely right, there does need to be a tutorial - I've never made one before though so that'll be fun to program ahaha