We know that meteors fall like missiles on the surface of the Moon as there is no atmosphere to 
protect it. Instead of water, comets and chunks of asteroids rain on the surface of the Moon and their impact creates craters. These are known as impact craters.
Craters are formed due to powerful volcanic explosions as well. When the Moon’s surface is pushed upwards by melted rock, hot lava and gases gush out of it, giving rise to craters. Some craters are more than two billion years old. Generally, the age of a large crater is determined by counting the number of smaller craters it contains.
Picture Credit : Google