Hi
Aleksandar's suggestion of a book is the one I'm reading and would recommend as well.
I would add that in order to get something useful out of ERP systems like NAV you do require knowledge of databases and a solid plan to get from a blank slate to something that will be working for the long term.
If you're trying to set up NAV for personal use, as a school project or something harmless it's all fine to be 100% self-taught, but otherwise you (or your company directors) should bite the bullet and get some professional help.