I really think that the best way to start is to use existing Demoniak3D code samples and demos ; this way you can try to tweak some parameters, add or remove things and so on, without knowing everything. For example, if you want to use smoke or add an ocean, you can start with a demo with those effects, to see how it works.
Actually this is how I did my "toon snow" demo available here :
http://www.ozone3d.net/demos_projects/index.php )
If you have any doubt on how to tweak a parameter, just take a look at the reference guide (
http://www.ozone3d.net/demoniak3d/devguide-v1/index.php?lang=2 ), and especially the "xml node reference" part.
The next step will be to take a look at demos using LUA scripting and GLSL shaders, and try to understand how they work. Don't hesitate to ask if you're lost !
