hi,
you can use MSDN Online you can find ALL about NAV on these pages ( (quickly updated)
General concepts
msdn.microsoft.com/.../jj672859(v=nav.71).aspx
by Departments
msdn.microsoft.com/.../hh879469(v=nav.71).aspx
by Processes
ex: Operations Planning
msdn.microsoft.com/.../hh173020(v=nav.71).aspx
NAV 2013
msdn.microsoft.com/.../hh173988(v=nav.70).aspx
NAV 2013 R2
msdn.microsoft.com/.../hh173988(v=nav.71).aspx
etc. etc.