Use the motion of the two planets to determine the value of k in Kepler's Third Law,
P2 = k a3, where P is the orbital period and a is the average distance from the star. Fortunately, all objects here orbit in perfect circles - not an entirely realistic scenario, but much easier to deal with.
The orbital period is given in years in the lower right corner, while the scale shown is the distance from the
star given in AUs (Astronomical Units).
The buttons can do exactly what they say - "Start" the simulation, "Stop" the simulation, "Restart" the simulation (set the time back to 0 and put the two planets on the starting line, and "New" gives you two entirely different planets. All of the planets are generated randomly, however they all obey Kepler's Laws and all orbit the same mass star - whose mass is not equal to that of the Sun.