It all began 75 million years ago, there was a federation in space ruled by the evil Lord Xenu, he thought the federation was to populated so he had aliens frozen. The frozen aliens bodies were loaded onto Xenu's cruisers, which look like BC-8's only with rocket engines. The cruisers then took the Frozen Aliens to earth and dumped them into volcanoes. The aliens weren't frozen- They were dead, the souls of those aliens however lived on.
They al floated up towards the sky, but the evil lord Xenu had prepared for this...Xenu didn't want their souls to return so he build giant soul catchers in the sky! The souls were taken to a huge soul brain-washing facility, that Xenu had also built on earth. There, the souls were forced to watch days of brainwashing matieral, which tricked them into lbelieving a false reality. Xenu then released the alien souls, which roamed the earth aimlessly in confusion, until the dawn of man which had bodies they could grab onto. They attached themselves to all mankind which to this day cause our fears, our confusion, and our problems.
Yes, this is what they believe in.