1) You need at least the commercial edition.
2) Since the GeForce GPUs support hardware T&L, which does the transform and lighting in hardware. Cause it's build into the hardware, it's fixed to certain effects. The shaders make the vertex and pixel processing programmable, therefore more flexible.
3) To programm a shader you need to write an assabler code which the GPU can understand/execute. If you just want to use it, it's shader specific what to do, normaly adding different skin maps is enough.