These distinctive features are believed to be the result of an asteroid, comet or meteorite impact with the Moon. Some of the craters on the Moon are so massive that if you stood at the centre of the crater you would be unable to see the rim the crater due to the curvature of the Moon's surface. Other craters are so small that they cannot be seen from the Earth. With a good telescope looking through the Earth's atmosphere the smallest crater you could see would be around 2 km in diameter. Unlike on the Earth where the atmosphere stops all but the largest collisions, on the Moon even the smallest meteorite will impact with the surface to form a crater. The craters on the Moon have remained the same since they were formed. Why do you think this is?
Image of a crater taken during the Apollo 11 mission