I also heard of Natural Stress Relief, what do you think about it, if you ever heard of it?
First, if you have to pay a fee, then do not go. Buddhist meditation conducted by true Buddhists should be free. As for "Natural Stress Relief" I think it sounds very commercial!
As I said before, there are as many types of meditation as there are sandwiches. As for Buddhist meditation, there are two relevant suttas explaining meditation by the Buddha. They are briefly described below, with references where you can click for details.
The most relevant is the Anapanasati Sutta.
This sutta points out the method to calm our mind by being mindful of our breathing. Another good reference is here:
With a certain level of this mindfulness and focus, the mind achieves full concentration or samadhi (http://en.wikipedia.org/wiki/Samadhi). At this level, the mind experiences tranquility which is Samatha. And the resulting experience from this state of mind is mental rapture or absorption which is called jhana (http://en.wikipedia.org/wiki/Jhana). The mind is now ready for further training to experience true insight into the true nature of things, vipassana (http://en.wikipedia.org/wiki/Vipassana). The practice of Vipassana is based on the "Foundation of mindfulness Sutta" or Satipathana Sutta (http://en.wikipedia.org/wiki/Satipatthana_Sutta).
So you see, the whole process is pretty complicating; and added to differing interpretations, it becomes mind boggling. As far as I am concerned, I practise Anapanasati which is mindfulness of breathing, and let the rest takes its course. It's that simple and easy!! To summarize: To achieve concentration is just like a person learning to drive a car; he needs full concentration to maneuver the car safely; this is samadhi. After a while he gains experience and can be relaxed while driving; this is samatha. Later, while concentrating and relaxing on his driving he can even enjoy the scenery around him and also engage in conversation; this is vipassana. Later he may become over-confidence and the danger comes!
As a parting comment, please remember that the above is my personal interpretation to the best of my experience and knowledge. There will be others who will disagree with me. So, please remember the Buddha's advice: use your own intelligence and common sense to decide.
Smile from justinchoo :-)