It sounds like you're looking for a Terragen Classic interface function. You may be referring to an outdated tutorial. There are lots of Terragen Classic (0.9x) tutorials around, so just make sure you're referencing the version you bought. Note that Terragen 2 tutorials are generally valid for Terragen 3, but the same is not true for Terragen Classic to Terragen 2 or 3.
- Oshyan