Hehe. Well, I haven't used C-Script in 11 years or whenever lite-C came along, but looking at the Gamestudio Wiki you can use regular DX9 shaders with it. Apparently, the postprocessing works the same as well, which is good.

Slin made some shader tutorial videos many years ago, I watched them but didn't get much from them (nonetheless they were my start into the world of shaders, so thanks for that!). You only need to understand the basic concept of rendering with shaders, everything else is straightforward (more or less) and learning by doing from there on.
For each vertex a vertex shader function is executed. It uses input such as position, texture coordinates, normals, does some calculations with them and writes the results in some registers. For every pixel on screen (not a texture pixel) when drawing a triangle a pixel shader function is executed where you can grab interpolated information from the 3 vertices (and vertex shader results) making up the triangle. On a very basic level this might be interpolated texture coordinates which you can use to sample a texture, for color, normal maps and all that good stuff.

Oh, there's an official tutorial I forgot: http://www.conitec.net/shaders/
Read "Introduction", "The D3D Pipeline", Workshop 1,2,5 for a start.
I have a default shader similar to the one from Workshop 2 and use it as a basis for most new shaders, no need to write it a new each time.