Welcome. Below you will find great references for beginning and advanced mappers and modders alike! I've found these references to be very reliable (and in most cases have used them extensively myself). If you cannot find what you need in these references, you may ask me something directly, too.

Modding:
http://wod.planetunreal.gamespy.com/tutorials/guide.htm // Really great site for learning and mastering UScript. If you can understand the "Beginners Guide to Uscript" then you're well on your way to using Uscript to your advantage! This site is great for beginners and intermediates.. check out their "All Inclusive Guide" when you have the time - you will not be sorry.

Mapping:
http://unreal.gamedesign.net/tutorials/basic/basic.html // A great site for beginning mappers. Wolf's tutorials teach you the basics.

General:
http://downloads.qoou.com/downloads/unrealed/CUERAG.zip // Simply THE BEST archive of everything you could ever want to know about mapping and scripting! This help file is comprised of the words of many experts, including tutorials, tips, and more. I still find things I never knew about (or mapping approaches not yet tested) in the "Complete Unreal Editor Reference and Guide".