Some good videos about NAV 2013 and NAV 2009 availables on Dynamics Community Blog

the videos are uploaded on youtube and linked on Community Blog

 List on Page:

https://community.dynamics.com/nav/b/navvideos/default.aspx

Nice example video:

How do i group data in microsoft dynamics nav 2013 reports

https://community.dynamics.com/nav/b/navvideos/archive/2013/04/29/how-do-i-group-data-in-microsoft-dynamics-nav-2013-reports.aspx