The source code listed in this book uses the Ext JS 4 SDK, available from the Ext JS website http://www.sencha.com/products/extjs/download. You need to download and install the SDK in order to run the code presented in this book.
Some chapters of this book present some tips and tricks that require Sencha SDK Tools. You can download it at http://www.sencha.com/products/sdk-tools/.
To create new themes, you need to have Ruby installed. Mac OS and some Linux distributions already come installed. If you are using Windows, you need to install it from http://rubyinstaller.org/. This book will also provide more details about how to install and use it.