The term "dark side of the Moon" is a popular but misleading phrase. In reality, the Moon does not have a permanently dark side. However, it does have a far side, which is the hemisphere that always faces away from the Earth. The reason it is called the far side is because we only see one side of the Moon from Earth due to its synchronous rotation, meaning it takes the same amount of time for the Moon to complete one rotation on its axis as it does to orbit the Earth.
Contrary to popular belief, humans have indeed been to the far side of the Moon. The Apollo missions, specifically Apollo 8, 10, 11, 12, 13, 14, 15, 16, and 17, sent astronauts to the Moon between 1968 and 1972. While the Apollo 8 mission orbited the Moon without landing, the Apollo 11, 12, 14, 15, 16, and 17 missions successfully landed astronauts on the Moon's surface. The Apollo 13 mission encountered a major technical failure and did not land on the Moon.
The reason why the far side of the Moon was not extensively discussed or publicized is mainly due to the limitations of communication during the Apollo missions. As the far side of the Moon faces away from the Earth, direct communication with the astronauts on the far side was not possible. To overcome this challenge, NASA placed a series of communication satellites, known as the Tracking and Data Relay Satellite System (TDRSS), in orbit around the Earth. These satellites acted as relays, allowing communication between the astronauts on the Moon's far side and the mission control center on Earth.
While the Apollo missions provided valuable scientific data and brought back lunar samples, including from the far side, the focus of public attention was often on the first human steps on the Moon, which occurred on the side visible from Earth. As a result, the achievements and discoveries made on the far side were not as widely highlighted. However, scientific research has been conducted using the data and samples gathered from the far side of the Moon, contributing to our understanding of the Moon's geology and evolution.