Of the four branches of Chinese medicine, I begin with the Chi Kung (Qi Gong) branch because it is my specialty. In 2003, I began learning under Grandmaster Victor Sheng Long Fu. In that time, I have spent well over $30,000, read and studied texts voraciously, and practiced, practiced, practiced my brains out. At different periods, I practiced more than six hours a day. I've made a lot of progress.
Kung Fu simply means "extensive practice." Chi Kung means "energy practice." There are 10,000 kinds of Qi Gong; but essentially, Qi Gong is an inward focus on posture and breathing. Mostly it requires movement, but sometimes it's just "standing," or holding a special position. The Shaolin monks even practice "Iron Qi Gong," which hardens their bodies almost unbelievably. I personally invite you to check out Iron Qi Gong on YouTube.com, but I beg you not to read about Qi Gong on Wikipedia (it's a train wreck, clustered with controversy and hyperbole).
The most important and developed forms of Qi Gong are the internal martial arts such as Tai Chi and BaGuaZhang. Do not shy away from them because they're related to "fighting." Energy practice of this kind is the most powerful means to optimize your health. As my teacher's father, Fu Wing Fay, once said,
"Tai Chi Chuan is a kind of profound art where you use your intent (mind) and not your strength. Therefore Tai Chi should not be looked upon as any kind of martial art. To look at it as such would deprive it of its art value and its philosophical foundation."
The practice of Tai Chi fixes the entire body. It mobilizes the joints and stretches them in all three planes, enabling far greater balance and mobility. The waist turning principle of Tai Chi massages the internal organs, while the slow, uber-relaxing movements ward-off stress and soothe the mind. The postural practice emphasizes moving the body weight onto the bones and connective tissue instead of the muscles. This in turn stresses and twists the bones, which stimulates the immune system (white blood cells are produced in the bone marrow).