As with every subject of study, the fundamental concept in chi kung is very simple. If one can't spell it out in simple statements, one doesn't know well. The fundamental concept is generate chi and cultivate chi through directing it to work.
From an energy perceptive, when a person's senses are deprived with stimulation, energy's outward channels will be blocked and it will be directed inward. It is a classical psychology experiment that when an experimental subject is placed in a room resting on a comfortable bed, inside a room with ambient temperature and deprived of visual and auditory stimulation, and further asked not to fall asleep, will result in hallucination - seeing things and hearing things. In chi-kung practice, the energy turned inward is made to transformed into chi. With the mind focused on the chi thus created and chi well managed by the practitioner, there will be no hallucination.
When a person meditates (seated or standing, i.e. zhan zhuang), keeping quiet and calm with a gradient, chi will be initiated. When chi starts to appear, the meditator's mind shall focus on the chi (he gazes at it with his mind). He can feel the process of chi creation. As in Tao Te Ching chapter 16: 致虛極，守靜篤。萬物並作，吾以觀復。(Reach the limit of emptiness, Keep absolute silence, Through my internal gaze, I experience everything being created). (Linkage here)
The next step of chi management is to guide it to perform work. In zhan zhuang, chi will be guided to fill evenly through the whole body, and any increase in chi will be distributed evenly inside the body. The feeling is muscles-as-one (肌肉如一）. As in Inner Cannon: 提挈天地，把握陰陽，呼吸精氣，獨立守神，肌肉若一 (Use your hands to hold heaven (head) and earth (feet) in position, balance yin and yang, use breathing to generate internal chi, keep stationery stand and practice calm internal focus, muscles to be connected as one unit).(linkage here)
And in classical Taoist meditation, the next step is guide the chi to do microcosmic circulation (小周天), the mechanics of which shall be explained in future posts, so stay tuned...