Apart from the online help (also available on msdn, see http://msdn.microsoft.com/en-us/library/jj552498%28v=nav.70%29.aspx), the new dimension structure is well described in blog articles:.
http://dynamicsuser.net/blogs/mark_brummel/archive/2012/09/30/dynamics-nav-2013-dimensions-i.aspx
http://dynamicsuser.net/blogs/mark_brummel/archive/2012/10/10/dynamics-nav-2013-dimensions-ii.aspx
http://blogs.msdn.com/b/nav/archive/2012/06/12/filtering-on-dimension-values.aspx
If encountering further issues with your addon for NAV 2013, check the online help for more changes in NAV 2013:
http://msdn.microsoft.com/en-us/library/hh173994%28v=nav.70%29.aspx
http://msdn.microsoft.com/en-us/library/hh174007%28v=nav.70%29.aspx
http://msdn.microsoft.com/en-us/library/hh169484%28v=nav.70%29.aspx