Since Autodesk went online with the help files years ago they are available once the software is available for download.  If you don’t want to download you can still check out the What’s New for most programs.

http://wikihelp.autodesk.com/Revit/enu/2013/Help/00002-New_in_Revit_2013

With the new Building Design Suites there is also a suites workflow.

http://wikihelp.autodesk.com/Building_Design_Suite/enu/2013/Help/0153-Suites_W153