If you want to know how the moon was formed, the experts guess it was created by a giant collision between two planets. This took place billions of years ago. You can find more information here: www.sciencedaily.com/releases/2010/06/10...

When the earth was growing there were also other smaller planetary bodies also growing. One of these hit earth late in its growing process blowing out rocky debris. A part of the debris went into orbit around the earth which would be the moon.