It is a meditation focused on awareness of the breaths. One observes the breaths, but does not try to control it. This form of meditation is in contrast to guided meditations, because the point of anapanasati is not to have anything on the mind, except awareness of the breaths, and especially no visualization. But with awareness of the breaths, it leads to deeper awareness of the body, and then to deeper and deeper truths. This meditation was taught by the Buddha more than 2500 years ago and there is a direct line of teachers from the Buddha to people today who teach the method (and from whom I learned). It is very easy to learn, but there are 16 stages of it. One you are able to complete one stage you can move to the next. I am on the first stage.
To do it, you just sit upright (it's better to do so on a soft surface, cross-legged, or in lotus position, but it can be done in a chair), and notice the breaths going in and out. You can focus on the feeling of the breath touching the nostrils and it goes in and out. If you get distracted by other thoughts, you simply bring the attention back to the breaths. It can be done lying down but it is not advised because it is about maintaining awareness and one can fall asleep or get distracted more easily lying down.
