Originally Posted by Tonakai

worldbuilder.lua

As you can tell by the name of the file, worldbuilder is a .lua feature.
So, to start with worldbuilder.lua, select Options from the menu, then choose Scripts. In the bottom of the .lua script list (might not if you have done/downloaded scripts), there is worldbuilder.lua. Click it.
Congratulations, you have now opened worldbuilder.lua. It should look like this.