What is the difference between “internal” and “external” martial arts? Bob Orland explains it in the chapter 10 of Martial Arts America in this way:

External systems and fighting arts emphasize strenuous physical training and conditioning as their primary methods for developing effective fighting skills. An externalist, for example, spends many hours conditioning his mind and body and toughening his knuckles, shins, and other personal weapons.

Although equally dedicated and vigorous in his training, the internalist spends much less time on toughening his hands and feet, and strenuously conditioning his muscles. Instead, he focuses on technical specifics and chi development. For example, an internalist trains continually to develop the optimal stance, precise weight distribution, proper timing, and best lines of force. This means that, among other things, his training regimen includes more slow practice routines than that of the externalist. Bringing all of these elements together perfectly is seen by the internalist as chi, or as the result of successful chi-power development.

(Regarding chi: Synergy or Chi cannot happen without timing, and timing is – as Parker put it, ‘complete synchronization of mind, breath, and strength.’.)

So internal martial arts focus on technical excellence and mastering the principles of effective body use. They leverage the strength of the structure of the body, gravity, and their understanding and sensitivity to achieve the maximal effect with minimal force and to bypass and neutralize their opponent’s force. Timinig, positioning, and angle are crucial. This skill is much more difficult than conditioning one’s body but can keep on improving the whole life. The key principles of effective body use relevant here are best described in Ralston’s Zen Body-Being: An Enlightened Approach to Physical Skill, Grace, and Power.

It might be easier to start first with an external system to learn the basics to be able to eventually perceive and appreciate the nuances necessary to make the internal approach work.

(See also the “External and Internal Application” section of the aforementioned ch. 10 for a good example.)