The use of the n-word among Black Americans is not something that white people need to really concern themselves with and certainly not arbitrate.
It is unsurprising that folks of all backgrounds would come down on different sides of the fence when it comes to the use of the word. With that being said, I think if you're white all you need to really know is "don't ever say it, or think about saying it, or allow other white people in your presence to say it" and then move along accordingly.
Hopefully this isn't a lightning rod response. Just my two cents.