Originally Posted by Kyross

Mountain you make with the height tool. Set width and depth, raise pressure, click raise and let fly...
Vehicles and CPs are objects you plane and give properties.
Textures are found in the shipped worlds folders. Usually called *_main_1.tga where * is the world (nab, tat, hot, etc...). Copy those to your world folder and when in the editor write the texture name in the box on the bottom of the left menu.
Sky depends on what you want to use. The geonosis sky comes applied to the map as it allows the most vehicles.