Corsix -> load CoH/OF mod (make sure you have the new version with OF support)
-> Load the Relic.module file (found in the main CoH folder)
-> go to data -> art -> presets. (Click the "+" next to it to expand the folder structure)
-> Right click the folder (presets)
-> Select "Extract all files in this folder"
Done.
Open Worldbuilder.
Under grass you can now load in the new "grass types".
(different types of grass, wheat, flowers)
Under atmosphere you can now load "preset" atmospheres from Relic maps.
(Browse around, try some out, untill you find a good looking one that fits.)
-> NOTE: Don't bother making your own atmospheres, too much effort and time for something that won't be as good as a Relic one
.
etc etc.