First you need to understand the difference between materials and textures. Then, second, it’s easier to understand how they relate to one another.
Materials: use two basic factors to come up with a given value; 1)The diffuse and 2) the specular.
Diffuse = diffusion… dic: the angular distribution of radiation by scattering.
In Lambert it uses only reflection, in O/N it uses reflection and roughness.
This defines only how much light is reflected by the material (equally smooth and polished silver and marble will reflect different amounts of light, just as polished silver will reflect more light than tarnished silver will).
Specular = specularity (dictionary is useless but it means) the way in which the reflectivity is scattered. In Cook/Torr and Phong it uses Spec and Hardnes and in Blinn it uses Spec, hard and Refraction
This uses the reflection value to define where and how much the light bounces back and how intense, confined and/or defined the specular quality (zones of high and low reflection) of the reflections are.
See this for better explanations:
So, the polished silver will reflect more light than the marble, but their specular values will be more alike than, say, that of hard plastic. Though the plastic may be just as smooth, its mollecules are bigger and so it scatters the light more and therefor has less hardness and less specularity (the area of specularity is wider and more diffuse whereas the silver has sharply defined highlights that shine like the twinkles in a diamond)
Now textures. They simply give color to the material. That is, unless you use their color values (MapTo Tab) to affect the material.
Nor: will affect Difuse and Spec values because it will progressivly wrinkle the surface as you increase the value thus progressivly scattering the light.
Csp, Spec and Hard: will affect the Specular value (Csp actually only the color).
Ref: will affect the Reflection
Obviously RayMir, Alpha and Emit will affect Diffuse and Spec, but their influence is global (across the whole object, or more correctly, across the whole of the material).
So, if a texture is set to Col, then only the Ref settings in the Materials Tab are used, but if it’s set to Col and Ref, then the whitest parts of the texture will reflect more than the Material settings and the blackest parts less. If you set the Ref setting in the Diffuse slider to 0.00, then the reflection values will be taken from the (greyscale) values of the texture… where the whitest parts of the texture are where the material will reflect, where the blackest parts are there will be no reflection, and in-between will reflect something in-between. This same principle applies to all the MapTo options; it allows you to map the diffuse and Spec values to to the material using textures.