Hi,
I'm sorry to hear of your difficulties. It sounds like you've seen Ryan Archer's tutorial here:
http://www.archer-designs.com/tutorials/usgs-elevaton-data-with-terragen-2/It's a good tutorial and is accurate although it does perhaps assume a little familiarity with the basics of TG2 such as moving the camera.
TG2 is not like other 3D apps in that the basic "set" is an entire planet, and this can lead to some wrinkles which might not be apparent with other apps. We generally suggest that you work around the origin of the planet though. Ryan's tutorial mentions this when he talks about changing the "Lat long at apex" parameter for the Planet object. The reason for doing this is that accuracy falls off as you move away from the origin. This generally isn't too much of an issue until you get well away from the origin though. Changing the apex of the planet ensures your area of interest has the highest accuracy.
There is a way to quickly view an element of scene such as heightfield. If you click the third button from the left under the 3D Preview (green circular arrow icon) you will see a menu item called "Centre on object or shader". Go to this and you can choose your heightfield from the submenu. You can also do this with the 3D Preview context menu (right click in the 3D Preview). This will centre the camera on the heightfield.
There are some things to look out for though. If you have not changed the "Lat long at apex" parameter for the Planet then the heightfield will be at its georeferenced location on the planet. First off, depending on where the heightfield is the camera may be inside the planet looking toward the surface where the heightfield is located. This could be what's causing everything to look black. A good way to tell if this is happening is that the "under terrain" indicator will be showing in the top left of the 3D Preview, under the compass. The indicator is a red version of the Terrain icon.
If you zoom out far enough you will eventually start to see the planet render again as you come out from "inside" it. If you can see the heightfield it might not be rendering properly anyway. This is why it's a good idea to change the planet apex.
So let's say you change the planet apex. The heightfield will now be sited at the origin and should be rendering ok in the preview. To see it you can again use the menu to centre the camera on it. This should show the heightfield pretty well, although you may be partly under its surface. You should see the "under terrain" indicator if this is the case, and you may also see broken up looking triangles in the preview. To move out from under the terrain you can zoom out. Rolling the mousewheel toward you is the easiest way to do this. In a future version the camera centreing behaviour is improved and this is less of an issue.
Here's my crash course to working with GeoTIFFs once they're loaded:
1) Copy one of the georeferenced corners from the Heightfield load node to the "Lat long at apex" parameter of the Planet node. You can use the buttons with the clipboard icons to copy and paste all the coordinates of a parameter at once.
2) Use the "Centre on object or shader" menu to centre on the heightfield
3) Zoom in or out if needed to see the heightfield
I will look into improving the documentation on using georeferenced heightfields.
Regards,
Jo