Why do you never see the far side of the moon from earth?

You can never see the far side of the moon from Earth because the moon is fixed in its orbit around the earth, meaning that one side is always facing Earth.
A common term for the side we can't see is "the dark side of the moon", but that designation isn't necessarily 100% accurate since the other side is lightened by the sun just as much as the side facing us.
Hope that helped! =)