SQL Server Professionals are lucky to have what I believe to be the most comprehensive set of product documentation available to them FREE from the vendor through SQL Server Books Online.
Added to that is the wealth of Community Content provided to us from Blogs and online information sources like MSDN, TechNet, MSSQLTips, PASS Chapter Websites, SQLServerPedia, SQLMag (etc...) and we really have no excuse for saying that we can't find info on any particular topic :o)
The latest Update to Books online has been released and is available here
My preference is to always have it installed on my local workstation in case the online (web) version is unavailable due to browser connectivity issues etc......