What is the difference between a material, a shader, and a texture? And why do they exist?
First of all, be aware that in some programs, there is no difference. For example, in Maya, a shader and a material are the same thing. Phong shader, Phong material, same exact thing. Such is true for other programs. However, a texture is completely different from either of these.
A texture is a 2D image pasted onto a material, basically. The material typically contains all the properties of how the model looks, such as the shader, color, opacity, glowyness (is that a word?) and so forth. The shader, generally speaking, makes the model look different. It can make the model pretend like it’s more detailed than it really is, or make it look like it’s on fire, or make it look like water is dripping down it the sides of it, or turn the model into glass, or a mirror, or whatever. There’s many cool things you can do with shaders. They are typically used to make objects more shiny, though.