Click a few points in the viewing rectangle to poke holes in the diffraction screen. Press the diffraction button to observe the diffraction pattern your point set generates. You can add the vertices of the regular polygons by pressing the button marked "D5." D5 stands for the fifth dihedral group. You see other dihedral groups by ajusting the scrollbar. The more holes you poke in the screen the longer the diffraction pattern will take, so I recommend poking no more than 7 holes.