The tutorial is about using a shader (which you can't in Extra) to
cover different areas with tiled textures.

Without the shader you may not use tiled textures (at least using
the fx_terraintex3). In that case you should skip the
"Create a RGB map to be used an texture map in MED" chapter
and continue with the chapter "Render the RGB-map".
You will then get a terrain texture map instead of a RGB map.

(To get different areas with grass, rocks etc, follow the instructions
in "Create a RGB map to be used an texture map in MED" but instead
of using black, red and green, use either different shades of green/brown/gray
or textures. You may here any numbers of sublayers.

You now have a RGB.bmp with a terrain texture instead of a RGB map.

Then in MED set this file a Skin0 and your done.

Cheers
Roland