You asked the 64-dollar question, Nick. “Naman” adds nuance to a sentence, but its exact meaning is very often contextual. In my learning of Spanish, it is similar to how elusive “llevar” is. Yet, “naman” is not a verb, but more like an adverb, so it could even be more elusive to one learning Filipino/Tagalog.
Sometimes it is added to soften the effect of a statement. For example, "Bakit mo kinuha ang pera ko?" (Why did you get my money?), with naman becomes, "Bakit mo naman kinuha ang pera ko?" In this case, the speaker could be saying, "May I please know why you took my money?" and that would be intended to make the question sound more polite or less confrontational. Yet, the meaning is still subject to the listener’s own interpretation.
We have this popular Christmas carol entitled, "Pasko na naman". Ordinarily, this translates to "It's Christmastime again/once more", which could simply be said as "Pasko na muli/uli." By using “muli” or “uli”, it only refers to Christmas coming every year. With “na naman”, it can be interpreted in the same way as “muli”, but can also mean that one is lamenting, maybe due to foreseeable and unavoidable expenses, that Christmastime is here again. So you need to know the lyrics of the song to determine which meaning the composer wanted to convey. Well, I’ll spare you the time to search for it and tell you that what the composer meant was that it happens every year and describes how it is celebrated. Maybe his reason for using the less clear “naman” was because it rhymes better with “na”.
So, giving you a definitive answer on how to best describe naman is practically impossible because its meaning can be subjective and contextual.
Iyan lang naman ang maisasagot ko sa tanong mo. :-)