Assigning a bitmap or procedural map to the Cutout component makes the material partially transparent. Lighter (higher-value) areas of the map render as opaque; darker areas render as transparent; and values in between are semitransparent.
Setting the cutout map's Amount to 100 applies all of the map. Transparent areas are fully transparent. Setting the Amount to 0 is the equivalent of turning the map off. Intermediate Amount values are blended with the original Transparency value. Transparent areas of the map become more opaque.
The gray levels of a cutout map determine the amount of transparency.
3ds Max opens the Material/Map Browser.
(If you choose Bitmap as the map type, 3ds Max opens a file dialog that lets you choose the image file.)
Alternatively, you can use the Slate Material Editor to wire a map node to the Cutout component.