The tutorial is a great place to start if you aren’t familiar with the language. It covers getting set up with Sass and the basic features of the language.
There are two books out about Sass (and Compass).
Sass and Compass in Action is a near-complete guide to everything Sass and Compass. It’s written by Wynn Netherland, Chris Eppstein, and Nathan Weizenbaum. Chris and Nathan are the current maintainers and designers of Sass.
Pragmatic Guide to Sass is a small beginners guide to Sass and Compass. It’s written by Hampton Catlin, the original designer of Sass.
Sass has a thriving community that’s eager to help out. There are several places where you can go to ask questions or help you debug problems. The Sass IRC channel,
irc.freenode.net, is a great place to ask short questions that you want answered quickly. Feel free to ping
nex3 if he’s there to get his attention quickly. If there’s no one on
#compass channel is worth trying as well.
If you have a longer question (or no one’s around on IRC at the moment), the Sass Google group is a great place to go. You’ll usually get a response within a couple hours or so.
If you’re having trouble or have a question, try the FAQ. If you don’t find what you’re looking for there, ask the Sass community.
Finally, if you want to look at the Sass implementation, check out the YARD API documentation. This probably won’t be too useful for most people, but if you’re writing Ruby code to interact with Sass, that’s a good place to look.