How does day and night occur?

The Earth rotates 360 degrees (1 full revolution) every 24 hours. The Earth rotates around the Sun. Therefore a part of the Earth will always have sunshine in it. The sunshine can only cover half of the Earth at one time due to Earth's round shape. Therefore the opposite side of Earth (not facing the Sun) will always be dark. Since the Earth rotates every 24 hours, the dark part will become light in an average amount of time of 12 hours. So if you were to mark one point on Earth, that part would experience an average of 12 hours of sunlight and 12 hours of darkness as it rotated throughout it's 24 hour rotation cycle. That is how night and day occur.