Press the arrow keys to move around the space. Try moving off of the sides!
Change the identification of the square's sides with the "Topology" dropdown.
Press t to leave a Tron-like trail behind your pixel, and press t again to discontinue and delete it.
(Unrelated but fun) Enter a number in the "Roots" input to plot the n'th complex roots of unity. (You can use these as the vertices of a graph and attempt various ways of connecting them with the trail!)