To create a map of a single color/intensity, click the New Map button, which is the first button above the Editor area.
In the New Map window, you can select the size for the new map at the left side, with the lock-shaped button constraining Width and Height to remain proportional.
At the right side of the window, you can choose which maps to create and their initial values.
Place a check mark in map names that you wish to create. By default only the currently active map type will be checked, but you can click Select All to check all maps.
Next to a checked map name, you can define the initial color or intensity for the new map(s).
Finally, click Create to initialize the new maps. Check the 3D Preview for a rendering of the new maps.
Another way to create a map is to extract it from an image or another map. For example, let's see how to extract a Displacement map from a {PBR?Base Color|Diffuse} map.
Start by opening an image in the {PBR?Base Color|Diffuse} Editor.
After opening an image in the {PBR?Base Color|Diffuse} editor, change to the Displacement editor.
Select the Extract tool at the top of the Map Tools area.
Hint: tools above the separator line deal with the extract or import of new maps, while the tools below will only be available if a map is open.
In the Method switch, select From Shading, as we'll be extracting from shading information in the {PBR?Base Color|Diffuse} map.
In the Source setting, select {PBR?Base Color|Diffuse} Map.
Extraction begins and a displacement map is extracted, which you can tweak with the settings that have appeared in the Extract tool.
Switch between the 3D and 2D views of the map, by clicking the button at the top-left corner of the Editor area.
Zoom the displacement map in and out by rotating the mouse wheel. Or try dragging while pressing the right mouse button to rotate. With the middle mouse button down you can pan the displacement map.
You may need to use the settings in the Extract tool to fine-tune the extraction: see the "Extract a Displacement Map" Guide in the Displacement section of the guides, for more details.
The following video tutorial covers map input/output: