Hold your phone up to the night sky and the constellations in that direction appear. Tap one and it opens the Greek myth behind it.
Point it at your feet too. The constellations that have gone around to the far side of the earth show up faintly. Winter constellations do not vanish in summer. They are under your feet.
To use the sensors, allow access to location and orientation. Even without it you can look around the sky with your finger. Use the mouse wheel or two fingers to zoom.