Ki is an eternal energy. It is also called Chi. It is inside everything, and can be used at a human's will. To use Ki, you must be able to visualize very well.
The key to using Ki is a place called the Hera. The Hera is located inside your body, 3-inches below your Navel. Visualize it as a swirling ball of green energy. This is where you are going to draw your energy from. To use Ki, You must visualize drawing energy from your Hera, and projecting it out of your body the way you want it to.