Material Operators, or MATs, are used for materials and shaders for 3D geometry.
A deep knowledge of computer graphics and rendering helps a great deal when working with materials and shaders. Without this knowledge, most users will be restricted to the basic settings of the Phong MAT and Point Sprite MAT.
Texturing and UV mapping geometry are involved processes, and the best results are often achieved inside dedicated modelling packages. The textured models can then be imported, and worked with, in TouchDesigner.
Many tools exist for modifying textures, such as the Texture SOP, but complex processes might be easier to achieve in a software package created for that specific purpose.