material, model are kind of self-explanatory
compile, decompile are too - convert the smd to mdl and vice versa
vtf export - convert tga to vtf
normal map - a map that can make a flat surface look bumpy, the engine interprets colors as depth. Basically it’s a very efficient way of making low poly models look high poly. the difference between bump and normal maps is that normal maps have direction, not just depth. See here and here. An example of the effect is here. It’s not a perfect technique, but it works pretty well.
Shaders are difficult to explain because there are so many types. Basically they’re what determines how things are rendered. Stained glass windows, the windows in portal, portals themselves, water, etc all make heavy use of shaders, but they’re just obvious examples. Absolutely everything uses shaders. And I mean literally everything, that’s just how source works. examples are $vertexlitgeneric for models and $lightmappedgeneric for world geometry, they’re the most common. See this and this for more info.