The Material Mapping section can be used to specify which material is mapped to which part of an object,
and how that material is mapped.
In the left drop-down list you can select the 'Part' of the object which you want to attach a material to,
while in the right drop-down list you can select the 'Material'.
With the controls below that, you can influence how the material is mapped to the object.
In the image above you can see a box made of 6 sides. The same material is mapped to each of the sides,
but you can adjust the position, rotation and scale of the material relative to the object it is mapped to.
In case of the selected side, we rotated the material -45 degrees over the Z-axis to create the 'slanted' effect of the planks.