"Aliens in my Lawn"     SOPack - Image Overlay Tutorial
  Overlay Essentials

This tutorial covers all of the basics necessary to use bitmap pictures as textures in Terragen.
Requires SOPack

"The Wall"     SOPack - Strata Tutorial
  Strata Essentials

This tutorial covers adding strata to Terragen images.
Requires SOPack

"Canyon de Chelly"     SOPack - Overlays, Strata and Masks Tutorial
  Advanced Overlays and Strata

This tutorial puts it all together and covers advanced mask creation using World Machine, creating seamless textures, and some of the finer points of tiling and texturing using SOPack Strata and Overlays.
Requires SOPack