Go to your NL install directory \environments\ and create a project file and folder; [projectname].env and folder [projectname]. You can create the .env by simply creating a new file and adding the .env extension, or by using save as in Notepad. Construction Kit also has an environmental editor, and there's also an older version around that includes a preview. (You'll have to look for both of them, they're very outdated, and people tend not to use them.)
In the .env file, simply use the commands listed in the sticky thread.
Of course, if you looked around the NL directory yourself, its not terribly hard to figure out how to do this. =) You do need to get started by creating textures and such though, so if you don't have any then your options are limited.