Three aspects of Qi within the human body

Qi Gong distinguishes three levels of qi within the human body; ‘essence’ (jing), ‘energy’ (qi), and ‘spirit’ (shen). Each of these different levels of energy are located in the three ‘dan tiens’ which translated literally means ‘elixir fields’. These are as follows:
The lower dan tien is the centre of our ‘primal essence’. It is located in our sacral area and is associated with our physical and sexual vital energies.
The middle dan tien is located between our heart centre and solar plexus, and is associated with our mind and our primal qi.
The upper dan tien is located in the centre of our brain (or third eye area), and is associated with our primal spirit.
The overall maintenance and health of these three dan tiens is one of the main goals of Qi Gong. It is said that the energy of our lower dan tien is depleted by excessive sexual release and physical activity. Our middle dan tien is depleted by excessive or negative emotions. Our upper dan tien or spirit is depleted by too much worry and thinking.
I would add to this that we can enhance the energy of our lower dan tien through balanced healthy use of exercise and sexual energy. We can enhance the energy of our middle dan tien by cultivating calm, positive and balanced emotions. Finally we can enhance the energy of our upper dan tien and spirit by cultivating calm, positive and balanced modes of thought and thinking.

Getting familiar with the three dan tien.
Basic standing postures are used in Qi Gong to develop and enhance the flow of qi to these three elixir fields. Here is a simple exercise that can be done in 5 or so minutes that works with all three of the dan tien:

First position
Adopt the basic Qi Gong standing posture, and adopt the basic Qi Gong breathing pattern.
See beneath your feet a ball of earth light, or earth qi, about a meter across. The top of the ball is resting on the soles of your feet. The bottom of the ball has a line of light extending deep into the earth. Breathe the qi from the ball into your body through your feet.

Second position
Now imagine that the ball of light rises up your body, to centre itself in your sacral area and lower dan tien. Raise your hands up in front of you so that the palms of your hands are 10-30cm in front of your sacral area, with the palms facing the centre of the lower dan tien. You should feel as if the palms are positioned around the edge of the ball of light, holding it in place. Breathe in and out of your lower dan tien a few times.

Third position
Imagine now that the ball of light rises further up your body to the middle dan tien. Raise your hands and arms up the body correspondingly, so that they are facing your middle dan tien, holding the ball of light in place. Breathe in and out of your middle dan tien for a few breaths.

Fourth position
Now imagine the ball of light rises further up your body to the centre of the brain, and upper dan tien. Raise your hands correspondingly so that the palms are in front of the face, holding the ball of light in place. Breathe in and out of your upper dan tien a few times.

Concluding
Having worked your way from the first position to the fourth in the manner described above, now bring the ball of light down from the fourth to third position, from the third to the second position and so on until you finish in the first position, back where you started.