I have not used the terrain editor in MED and don't know about any
tutorials on that one.

That was the bad side. Now to the good side.
I currently writing a tutorial on how to get att Terragen terrain up
and running in 3DGS and will publish it on the Wiki this evening.

Edit:

The first part about Terragen is done and can be found here in the Wiki under
the Content Creation Tutorials / Level design tutorials. Will add some context
about the MED import later this evening.



Kindly
~Roland