Hi ChristopherM
There really isn't a quick start guide, but the User Guide should be helpful. For the quickest start you're probably gonna get, read the "Getting Started" section. For a more detailed explanation of the features and functionality of SONAR, see the extensive Help available in the Reference guide/manual. For a better start go through the "Getting started" section in the Reference Guide and read the "New Features In SONAR X3" section. Then, eventually, read the entire Reference Guide. :) Here's the link to download the User Guide and the Reference Guide:
http://www.cakewalk.com/Support/kb/reader.aspx/2007013322 SONAR X3 is complex software with comprehensive features an impressive functionality for sound authoring and music production, so reading the "Getting Started" section of the User Guide is about as quick start as you're probably gonna get. There is so much put into this software package, which means there's a lot to learn. However, seeing how powerful SONAR is, that's a good thing, as there is so much you can get out of using SONAR. There's a learning curve, but it's really an exciting adventure.
Happy learning and cya around.