な is essentially "da", the copula. The "da" is usually changed to na, when something follows the copula. な can be considered the colloquial equivalent of the renkai-kei de-aru form (however, the usages for "な" and de-aru are not necessarily the same, but guess that's for another discussion)
Anyway, here are some examples
atashi ha gakusei na no-de, gakkou ni ikanakeryanaranu (Because I am a student, i must go to school)
Note that "atashi ha gakusei da no-de" would be technically grammatically correct, but in modern Japanese, da would always be changed to な
kare ga chikan nandakara (formal: na no dakara), saketa hou ga ii. (It is because he is a molester, avoiding (him) is better)
Note that na is usually before things like "no-de" and "no-da", where as "da" is followed by "kara" or "kedo"... A little memorization is needed to remember which goes before which, but shouldn't be too difficult.
Just to clarify... if you want to say "because he is a molester", just using "dakara" would suffice. However, if you want to say "IT IS because that he is a molester", then probably "nandakara" would be more appropriate.