This is a great guide, but I'm having a little bit of trouble with it. Can someone help with the mountain part of the tutorial? I'm stuck on the "mountain mask" step.

Specifically this part:

Quote Originally Posted by RobA View Post
[B]
Use the magic wand again to select the non-mountain area (like with the land) and create a new layer called “Mountains Mask” with a white on black. (Also the white colour selection as a new selection mask using Select->Save to Channel).

Now we want to create a heightfield from this. The easiest way I have found to do this is to copy the current visible image (Edit->Copy Visible) then paste it (CTRL-V) to a floating selection. Click the New Layer button to get it on its own layer rather than a floating layer. Now stretch the colour range out (Color->Auto->Normalize):
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Does it mean to create a black background and fill the selection with white, then create a channel with only the white part selected? Also, what is the "current visible image" that I need to select, is it the black/white mask layer or the detailed clip layer?