shaders question (3DS Max involved)

I'm trying to learn about shaders, but the information I've come across is kind of hard for me to understand how to apply it to what I'm trying to do. I'm trying to learn how to make code for new shaders that will allow me to add a larger variety of texture maps into Unity. I have background in coding, but right now in my company, I'm working primarily with 3DS Max, and I don't know much about how adding texture maps in Unity works. So I guess essentially my question is, first of all, could someone explain to me how adding texture maps in Unity works? (I haven't worked much with Unity before; I mostly just learned how to code outside of it). Secondly, what information do I need to know to go about learning how to code new shaders that will allow me to add a larger variety of texture maps from 3ds max into Unity? And finally, does anyone know of a good resource, or multiple resources, that will further help me to accomplish this goal? (Resources for learning HLSL or GLSL would be a big help, too!) :)