Material Editor > Right-click a Type button, sub-materials button, map button, bitmap button, or color swatch.
Elsewhere in the user interface > Right-click a map button or color swatch.
A set of right-click pop-up menus in the Material Editor (and elsewhere in the program's user interface) lets you copy and paste, and otherwise manage materials, maps, bitmaps, and colors.
You see these menus only if copy and paste actions are appropriate. For example, if you copy a material and then right-click a map button, nothing happens.
When you right-click a button that represents a material, this menu appears. This includes the Type button for a material, and sub-material buttons such as you find in the Multi/Sub-Object material, the Blend material, and others.

Cut—Makes a copy of the material. If you right-click a sub-material button, this also removes the material from that sub-material component. If you right-click the Type button, Cut is equivalent to Copy.
Copy—Makes a copy of the material.
Paste (Copy)—Pastes a copy from the copy buffer.
This item doesn't appear if you haven't yet copied a material.
Paste (Instance)—Pastes an instance from the copy buffer.
This item doesn't appear if you haven't yet copied a material.
Clear—If you right-click a sub-material button, Clear removes the material from that sub-material component without making a copy of it. If you right-click the Type button, Clear has no effect.
When you right-click the button for a map component (a “map slot”), the menu you see depends on whether a map has been assigned yet.
The following menu appears if a map has been assigned:

Cut—Removes the assigned map, and puts a copy of it in the copy buffer.
Copy—Copies the map without removing it.
Paste (Copy)—Pastes a copy from the copy buffer.
This item doesn't appear if you haven't yet copied a map.
Clear—Removes the assigned map without copying it.
Open—For bitmaps, launches whichever application is associated with the currently assigned 2D map.
This item does not appear for other map types such as procedural maps.
Reveal Location in Explorer—Launches a copy of Windows Explorer to display the folder where the map is saved.
This menu appears when you click a button that specifies an external bitmap. See Bitmap 2D Map.

Paste—Pastes the bitmap from the copy buffer.
Open—Launches whichever application is associated with the bitmap.
Reveal Location in Explorer—Launches a copy of Windows Explorer to display the folder where the bitmap is saved.