Now even if this is your first trip into the Terrain Editor, don't worry. Your screen may not look exactly like this shot of mine but most of it will be visible somewhere.

For now, click on the black triangle at the far end of your 'Terrain Canvas' (1). In the drop down menu, click 'solid' to make your terrain solid (2). Otherwise Bryce leaves it looking hollow on the inside. This doesn't always matter but I tend to make all my terrains solid. Perhaps I just don't like the idea of insubstantial mountains in my pictures ;)

Now click on the grid shape at the bottom of the tools bar (3). Here you can set the resolution of your terrain. I set it to 512 here.

Detail:
This affects the number of pixels in the greyscale image that tells your terrain what shape to be. A low resolution of 64 for instance will give you the same shape but made up of so few pixels that the terrain will look very jagged and unnatural. The default is 128 and I tend to switch up to 512 or 1024 for most of my work. However, I switch up and down as part of the shaping process as you will see. Sometimes it's worth staying at 512 while doing things which take a lot of calculation such as looking for a new fractal for your mountain shape. At 1024 it can take so long to recalculate your terrain that you may think the computer has 'hung' or stalled. It hasn't (usually anyway) so just be patient and leave it. It may well take anything from two minutes to half an hour if you're at very high resolutions and have a slow processor on your computer.

Tips on saving your work:
Save your file early on. Save it with a name like Mountain1. Every time you make a change that results in something you like, choose 'save as' and the next file will be saved as Mountain 2, Mountain 3 and so on. This means that any time you decide you took a wrong turning in your work, you can go back to a previous version and start again.

In addition, something I do while building mountains, trees or anything Brycean, I make a copy within the scene using Ctrl D. I rename it something imaginative like terrain 1 spare in the attributes box. Then I either 'hide' it using the hide option in the attributes box or else I move it out of sight of the camera. That way, I always have an original or two handy if I decide I didn't like what happened and want another go. Or if I want a similar but not identical mountain to the one I have and this provides a good seed to move on from.

(And yes… leave lots of room on your hard drive or be very good at housekeeping and delete all those files before they start spilling out of your screen all over your keyboard.)