Knapping can be an incredibly complex art that can require years of experience to create beautiful and functional tools. But knapping, in its simplest form, is banging two stones together causing one to fracture and create a sharp edge. That edge could be used as a crude tool as it is. Probably 80% of the tasks you would need to tackle could be done with that edge. The next 15% of refinement would probably take weeks or a few months to learn and the last 5% of refinement may take years. So for simplicity, let’s focus on what you need to know to create a tool that would do 80% or more of what you need done. If you were to bang enough stones together, you would eventually figure out the two most important things about creating a predictable flake:The Cone and The Platform.
The Cone: The type of stones used in knapping have a conchoidal fracture. (If you aren’t sure what types of stones make good tools, read this entry) Conchoidal fracture means that the instant the blow strikes the surface it is transmitted into a cone radiating at about 100 degrees.This cone (also called a Hertzian Cone) determines at what angle you must strike a blow to remove a particular chunk of stone. 
If you only had to know one thing about knapping this would be it. The images show a stone core being struck at the correct angle to produce the desired flake and at an incorrect angle in which the cone radiates too deeply into the core.
Striking the blow correctly (as shown at left) aligns the edge of the cone with the flake you want to remove. The chances you will get the desired flake are good.
Striking the blow at the wrong angle(as shown below) causes the cone to penetrate too deeply into the core. The chances you will get the desired flake are very poor.
The platform:The platform is the point of impact on the core stone. What is important is that the platform allows the shockwave to travel along the stone and create a fracture in the direction that you want.You are going to hit the stone somewhere and you just want to make sure that the somewhere is going to be conducive to transferring the energy in a direction that you want. That may mean shaping the platform by chipping or grinding so that you have a suitable point of impact. The image below shows a poor (non-existant) platform. The blow will just glance off the core because the platform doesn't exist.
References:
Is a great primer on the subject and a good place to start for the beginning knapper.
"Flintknapping – the art of making stone tools" by Paul Hellwig.
Is one of the best books out there but it has so much depth that it will probably just frustrate the beginning knapper.
"The Art of Flintknapping" by D.C. Waldorf
Video Resources:
This is a great series that should help you get started.
