Explain why a compass points in a north-south direction?

a compass is a free-spinning magnet. When it interacts with the magnetic field lines of the earth, if the compass is not parellel to the field lines, it will spin. Just like a weather vane will move if it isn't parallel to the wind, the magnet will experience a force from the field lines causing the needle to move. When the needle is aligned with the field lines, it has reached an equilibrium since a deflection either to the east or west will experience a force pushing the northern half of the needle to north.

So, essentially think of the magnetic field lines as a north-south wind and the magnet as a weather vane.