We start to move toward simplicity in this meditation. The three stillnesses are stillness of body, stillness of speech and stillness of mind. It is a profoundly simple method that uses stillness as a meditation method. This covers the three types of actions we can make to effect the world. Bodily actions, speech and thoughts. When the stillness of these three things is experienced it is a gateway to a sublime and transcendent type of stillness and peace.

The key to this meditation is the non-doing and the noticing. You are not doing things like moving, talking or following thoughts and it is important you notice these things as a tangible presence. They are not just nothing; by noticing the three stillnesses you bring stillness to life and directly experience a new dimension of your being.

Further Reading:
A Master Explains a Short Cut to Inner Peace and Stillness ~ Tenzin Wangyal Rinpoche
9 Stages of Training the Mind ~ Sakyong Mipham Rinpoche