One of the most important features of OpenGL is the ability to simulate light. Ambient lighting is used for the radiant effect in lighting. It represents a fixed-intensity light source that affects all objects in the scene equally. Diffuse lighting is the re-emission from a surface. A "non-shiny" surface which re-emits everything that hits it (like snow or rough wood) would have a very high diffuse lighting value.
There are some more lightning features in OpenGL. For example, your illumination does not only depend on the light configuration but as well on the configuration of the material, which is done in the design.
The personalization of the basic variables is possible. That is the light position (Scrabble3D has only one source) on the x,y, and z-axis. And below you have access to the intensity of ambient and diffuse light in percent.
Mipmapping is a technique for antialiasing of textures in relation to their distance. It means that textures are pre-calculated, optimized sequences of textures, each of which is a progressively lower resolution representation of the same image. Try to switch it off if you don't like the blur side effect.
With the option transparent board the texture of the board is either opaque, that means you cannot see the actual board behind the square, or transparent.
The last option reflective board simulates a polished board. The board will reflect pieces if this option is set.