The Moon only shows one side, the near side, to the Earth, while the other side, the far side, remains mostly hidden from our view. This phenomenon is known as tidal locking or synchronous rotation. It occurs because of the gravitational interaction between the Earth and the Moon.
The gravitational forces exerted by the Earth on the Moon caused the Moon's rotation to gradually slow down over billions of years. As a result, the Moon's rotation period matches its orbital period around the Earth, causing one side of the Moon to always face towards us.
The part of the Moon that is not visible to us, the far side, is not completely dark or invisible. In fact, it receives sunlight just like the near side. However, since we cannot directly observe it from Earth, it is often referred to as the "dark side of the Moon," even though it experiences day and night just like the near side.
To study and explore the far side of the Moon, space missions have been sent specifically to investigate this region. For instance, the Chinese Chang'e missions, such as Chang'e 4 and Chang'e 5, have successfully landed and operated rovers on the far side of the Moon, providing valuable information about this unexplored area.