The sun does not actually rise in the east and set in the west. It is the Earth that is rotating on its axis from west to east. As the Earth rotates, different parts of the Earth are exposed to the sun’s light. When the Earth rotates so that a particular location is facing the sun, it is daytime in that location. When the Earth rotates so that a particular location is no longer facing the sun, it is nighttime in that location.
The sun appears to rise in the east and set in the west because we are standing on the Earth and rotating with it. As we rotate, the sun appears to move across the sky from east to west.
The sun only rises due east and sets due west on two days of the year: the spring and fall equinoxes. On these days, the Earth’s axis is perpendicular to the plane of its orbit around the sun. At other times of the year, the Earth’s axis is tilted, so the sun appears to rise and set slightly north or south of due east and west.
The tilt of the Earth’s axis is also responsible for the seasons. During the summer, the northern hemisphere is tilted towards the sun, so the sun appears higher in the sky and the days are longer. During the winter, the northern hemisphere is tilted away from the sun, so the sun appears lower in the sky and the days are shorter.