Is it most like JED or Worldcraft? I was pretty good at both but I've never touched Radiant.
Xeph, read some of the tutorials and FAQs posted in the Radiant Resources (
http://www.jediknightii.net/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic&f=11&t=000002) thread to find out about Radiant.