Some YouTube links that demonstrate some aspects of Dynamics Nav.
Just some examples.
Just search Dynamics Nav followed by the functionality required and you will find a video.
Very useful list of functionality demonstrated from one web site. Match Business Solutions.
Some specific demos:
1. Basic functionality for Nav 2013r2.
2. Processing sales and purchases on Nav 2013r2.
3. Workflow in Nav 2016.
4. Fixed assets in Nav 2015.
5. Prepayments demo in Nav 2009
6. Cash flow in Nav 2013
7. What's new in Nav 2017
8. Module and functionality review in Nav 2016
Other interesting videos:
Dynamics 365 tour
Power BI tour