Sass and Compass are Ruby gems, which are Ruby package managers. Prior to the installation of these gems, we need to install Ruby.
If you use Windows, go to http://rubyinstaller.org/ and download the latest version.
If you use Mac OS, you do not need to worry, because Ruby comes installed on Mac OS. However, on the Sencha website, they recommend that you install XCode (it installs all required dependencies); to install XCode, please go to http://developer.apple.com/xcode/.
If you use Linux, well, there are several Linux distributions available today, and the best way to install Ruby is to use the default package manager for the particular distribution that you use.
Debian, Ubuntu, and other Debian-derived ...