Not aware of any tutorials on the subject, but.....

Yes, Carrara can use Grayscale images to create terrains.  Start with an empty scene, then drag in a Terrain object via the tool icons or front the Insert Menu drop-down.

That will get you into the terrain editor, from where you have lots of options in creating a terrain using the tools in the editor.  If you're not comfortable with the painting tools of the editor the you can Clear the canvas using the 'Clear' button and 'Import'  a height map  or displacement map available from numerous sources on the Web to generate a terrain, real world or otherwise.  First thing I would do though, is READ the MANUAL.  I know the documentation sucks, but even the Carrara 6 Manual that comes with Carrara 8 has a wealth of info that will help