How exactly the Moon was formed remains a great mystery. The moon is visible in the night skies with our naked eye, and as such it's pretty hard to ignore, but there are so many different theories as to how it got there.
On the other hand, one of the latest theories that's gaining a lot of traction is how the Moon could be made up of several other space rocks that have impacted the Earth and kicked up debris into a dust ring around the planet, which allowed a Moon to form from the materials.
Adding to all the confusion, the Earth and the Moon have very similar isotopic and elemental makeups, which suggest they were made out of the same materials by something large slamming into the Earth and kicking up large amounts of material from the Earth into space.
While it remains a mystery, all current theories have their ups and downs and require additional research and insight to better understand how the Moon may have come to be.