Heres a link to the underworkings of meditation, for those who have taken martial arts in the past you should know the basics already but for everyone else this is a good read.
How Meditation works.
EDIT: I just realized that this is one of the first articles that delves in to the idea that religions such as Christianity performing meditation. "Through prayer you will find god" Well My religious friends, Prayer if done right is not very different than meditation. So don't thing meditation is devil worship... For the devil does not exist.