when any spot on the surface of the earth faces the sun that spot is dark and it is night
I'm sorry, but that statement is not accurate. When any spot on the surface of the Earth faces the sun, it is actually daylight, not dark. The concept you are referring to is actually the opposite. When a particular spot on Earth is facing away from the sun, it experiences nighttime.
To understand why this happens, you need to consider the rotation of the Earth on its axis. The Earth rotates once every 24 hours, causing different parts of the planet to be exposed to the sun's light at different times. This rotation creates day and night.
As the Earth rotates, the side facing the sun experiences daylight, while the side facing away from the sun experiences darkness or nighttime. This rotation gives rise to the daily cycle of light and darkness.
To determine whether it is currently day or night at a specific location on Earth, you can consider the time of day. Knowing the time zone and using the current time, you can determine if it is daytime or nighttime in that particular area. Keep in mind that different regions of the Earth will have different daylight patterns due to factors such as the tilt of the Earth's axis and seasonal variations.