Getting started tutorial:
http://www.freewebs.com/andycr/realityfactory1.htm
RF FAQ:
http://terrymorgan.net/rffaq.zip (it may be long, but reading the entire thing will help alot)
Complete RF E-book, though out of date:
http://dhost.info/realityfactory/downloads/m3drf.zip
RF Manual:
http://dhost.info/realityfactory/onlinehelp/index.htm
Reading all of these will take awhile, but after you do, you'll be making games in no time flat. I have listed them in the order I reccomend you read them, top first, bottom last. The first will get you up and running with RF, showing you how to make a basic level. The second will give answers to alot of common questions. the third will show you many aspects of RF in-depth, and the fourth will teach you almost everything about RF, and should be used quite often as a reference while making games.
Welcome to the forums, and happy game development!
(Also, if you are only looking for world editors, do you mean to make your own worlds, or to do above and also import them into a different game? If the first, RF's what you want; If the second, you might be better off with one of many free editors, such as QuArK, or the editor that comes with the game you wish to make levels for.)