Some good tutorials on getting started creating Tridion GUI extensions:
- http://yoavniran.wordpress.com/2011/03/03/setting-up-a-tridion-gui-2011-extension-in-8-steps/
- http://www.curlette.com/?p=279
- http://code.google.com/p/tridion-2011-power-tools/wiki/nononsenseguide
- http://tridionfanboy.wordpress.com/category/javascript/
- http://www.curlette.com/?p=401
There are also plenty of existing extensions to be found on SDL Tridion World that serve as great material for studying. Finally: never underestimate the power of studying the source of Tridion's GUI yourself. The JavaScript parts are readily readable on your disk and (if you disable the default JavaScript minification) also in your browser.
