A heightmap is a grayscale image that represents the elevation or height of a terrain surface. Unreal Engine provides built-in support for importing heightmaps as a way to create realistic terrain surfaces. Here are the steps to use a heightmap in Unreal Engine:

1. Create a 3D Map of the desired area and download the Texture and Heightmap set. If you need you can use the 16 bit option in the exporter.
2. Import the heightmap image: In Unreal Engine, select “Import” from the “File” menu, locate the heightmap image, and select it. Unreal Engine will import the image as a grayscale texture.
3. Create a landscape object: In the Unreal Editor, select “Modes” -> “Landscape” to open the Landscape tab. In the Landscape tab, select “New Landscape” to create a new landscape object.
4. Assign the heightmap to the landscape object: In the Landscape tab, select the “Import” button in the “Heightmap” section. Select the imported heightmap texture as the source for the landscape height data. You can also adjust the “Z Scale” value to control the height of the landscape.
5. Adjust the landscape settings: In the Landscape tab, you can adjust various settings for the landscape, such as the resolution, size, and material. You can also use the “Sculpt” tab to sculpt the landscape manually or apply textures and vegetation to it.
6. Save and use the landscape: Once you’re happy with the landscape, save the scene and use it in your game or project. You can also export the landscape as a heightmap or mesh if you need to use it in other software.

That’s it! Using a heightmap can be a quick and easy way to create a realistic terrain surface in Unreal Engine.