Why do the stars seem to turn around one star in the north?

The stars seem to turn around one point because you are turning. Earth spins once on its axis, and from the ground that spin makes the whole sky appear to swing around the two points where the axis, extended into space, would poke through. In the north, a bright star called Polaris sits within one degree of that point. It is the pole star: it hardly moves, while every other star traces a circle around it.

This daily swing has a name, diurnal motion, and it is caused by Earth's rotation. Almost every star appears to follow a circular arc, which is why photographers can leave a camera open for hours and get a picture full of concentric rings. Point it north and the rings are centred very near Polaris. The stars that never dip below your horizon go round counterclockwise.

One turn takes 23 hours, 56 minutes and 4.09 seconds, a sidereal day. That is almost four minutes shorter than the day between two sunrises, because Earth is also travelling around the Sun. So each night a given star rises about four minutes earlier than the night before, and the sky quietly shifts with the seasons.

Star trails can even be photographed from orbit: in 2012 astronaut Don Pettit made them from the International Space Station. And because Polaris stays above the north point of the horizon, at a height roughly equal to your latitude, it is a natural signpost for finding north.