Bringing in Atlas Terrain

#1 First you need to export it from L3DT to Atlas format. If you have L3DT Pro (bought it from GG here) then simply select File > Export > To Torque Atlas. Generally, the convention is to put it in data/terrains folder. After that, I've found the easiest way to put it in your game is to edit the mission file. So crack open the MIS file you are trying to load and add something like this:

new AtlasInstance2(NewTerrain) {
      position = "0 0 0";
      rotation = "1 0 0 0";
      scale = "1 1 1";
      detailTex = "~/data/terrains/details/detail1";
      atlasFile = "~/data/terrains/YOUR_TERRAIN.atlas";
      lightMapSize = "1024";
   };