To play a solo game click Quick Start or to play against another person, click Manual Setup. Then while one player looks away, click on the centre squares to place/remove atoms and click Start when done.
Click on the edge squares to fire rays or on the centre squares to place/remove atoms. Click Declare Molecule when you think you have accurately placed all the atoms.
Your score starts at 100 and reduces by 1 for each ray marker placed and, at game end, by 10 for each incorrectly placed atom.