a) な (na) adjective – are followed by な (na) and the noun.
One main diff is that な (na) adjective can directly modify a noun following it by sticking [な (na)]
b) Example sentence without [な] – After a noun – [noun] + [adjective] + [ です desu] :
b.1) この 本 は たいせつ です。(this book is important)
c) Example sentence with predicate – Before a noun – [adjective] + [な] + [noun] + [です desu] :
c.1) これ は たいせつな 本 です。( this is an important book)