A material tells a surface how to behave when light interacts with it. Does the light pass through, does it reflect, does it get absorbed? If you modeled a cup without a material and hit render it would just look like a cup shaped object with a solid flat color. A material can make that geometry behave like anything from polished glass to old, weathered wood.
The VRayMtl node is a blank canvas material that is specifically designed to work with V-Ray. All materials that you will create will use this node. It allows for physically correct illumination in a scene with faster rendering. This material can be easily set up to simulate a huge variety of surfaces from plastics to metals to glass and more by adjusting a handful of parameters.
Furthermore, with the VRayMtl you can apply different texture maps to parameters, control reflection and refraction, add bump and displacement maps, and much more. Learn more about V-Ray Materials here.
a. The basic elements that make up a material are:
Diffuse – The base color or pattern that defines the object, i.e. is it green or blue?
Reflectivity – How much light it bounces back. Does it have a mirror finish or is it dull?
Reflective Glossiness – The clarity of the reflection and highlights seen across the surface.
Refraction – How light bends as it passes through a transparent object (not the same as opacity).
Refraction Glossiness – The clarity of the refractions seen (think clear or frosted glass).
Bump – The surface characteristics that give it texture you can feel. Wood grain, fabrics, scratches, etc.
BRDF Shader – How the highlight behaves (crisp edges or soft and feathered) in the rendering engine.