Do I really need to answer this?
Pressure created by centrifugal forces and centripetal forces from the snow/ski interaction. Also turning and gravity create some of these forces.
If you are patient and accurately guide the skis to an edge, they will interact with the snow, and begin to turn. The guide to an edge will require turning your femurs in the hip sockets (passive rotary if you will) as the skis engage and begin to turn and bend, there will be forces being built up as well. If you don't balance against the pressure or push back (manage) with correct amount, you will upset the balance. tdk6 shows the balance skills to keep from falling over. Physics tell us the weight will go to the outside ski. Trying to push too hard on the inside ski will also upset the balance. Just bracing against the forces will almost always cause the ski to break away. By relaxing or letting go of some of the pressure, you dissipate some of the energy (also a form of managing pressure)
By learning to "feel, and adjust" to what the terrain, snow, and skis throw at you, you can make the turns more and more efficient.