Links to 20 or so Terragen2 tutorials hosted on Devientart
These links will take you to TG2 Tutorials hosted on dieventart written by many different TG2 artists. The tuts include step by step, and tips and tricks. Most of them require a basic understanding of TG2, but a few are for beginners.
Main list with more than 20 tutorials. http://ladyofspira.deviantart.com/journal/Terragen-The-tutorials-214154377
Fog and Sandstorm: http://hammerz.deviantart.com/gallery/?offset=48#/d5ul0d
Seeing Through Water: http://hammerz.deviantart.com/gallery/?offset=48#/d5ul1u