It's actually tilting over by about 23 degree.In our summer,the north pole is pointing towards the sun so the sun rises and sets roughly from due east to due west. In winter,the Earth is on the other side of the sun so the North Pole is pointing away from the sun.This means the sun rises and sets more towards the southeast and southwest.You might notice this as you look out of the window.Think back to how high in the sky the sun was during the summer.Compare this to where the sun is during the winter and you'll see it's much lower down towards the horizon.There's less distance for it to travel so the sun rises later and sets earlier meaning there's less daylight.