It might be hard to find where to use fresnel angle calculation. This is the angle forme between the vision ray and the surface normal. It is useful to simulate the reflection of many surfaces. When we are near a water pool, for example, we can see the pool bottom if we look downwards, but farther away we can only see reflections. The same happens with glass in architecture. With the image above, it should be easier to understand how to use this effect. Use the "Blend" factor in the "Layer Weight" node to control Fresnel force.
June 04 2013