As a general word of caution, if you have no experience with Cisco or other CLI based router admin (such as linux and red hat derivatives), I would not recommend diving in unless you have a lot of spare time on your hands in the event that you accidentally delete all routing tables or cause other serious problems!

Even in a professional business environment, due to some differences between IOS and hardware versions and the need to reboot for some settings to take effect, it’s always a good idea to perform changes after hours when critical business operations will not be interrupted by internet or service downtime.

Official Cisco IOS Manual, http://www.cisco.com/en/US/docs/ios/12_3/featlist/sec_vcg.html

Manipulate NAT and other general help references and top hits on Google for common Cisco beginner questions:
http://www.nthelp.com/handy_cisco.htm
http://www.loeppenthien.dk/Network_IOS.asp
http://www.simulationexams.com/tutorials/ccna/cisco-ios.htm
http://www.networkclue.com/routing/Cisco/IOS/index.aspx
http://www.oreillynet.com/pub/a/network/2002/01/02/ciscotips.html
http://portforward.com/english/routers/port_forwarding/Cisco/Cisco800Series/default.htm