This node has changed drastically due to the new shading model using by LightWave 3D 2018.
It modifies the weights for the component channels used later on by shading and allows you to boost them (changing their contribution to the material) as well as changing their colours using blend modes.
All remaining inputs correspond to the controls in the user interface.
Andrew Comb use the Material Tweaker alongside other free db&w Tools in his Advanced Shading Tutorial presented at the San Diego LightWave Users Group.