The novel opens up with a Montag that appears to be confident, enthused, insensitive, and gleefully overjoyed by his job, life and role in burning books. He whistles while walking home from work; he smiles in his sleep; he laughs around the bonfire of books like a man with no worries. However, at the very end of his first conversation with Montag, Clarisse asks, "Are you happy?" At first, Montag thinks it's an absurd question, but once in the house, he realizes that he in fact is not happy at all. The confident exterior fades, and his more introspective, insecure and questioning side comes out.
Bradbury hints at these other dimensions of Montag's character in a couple different ways. First, Bradbury uses foreshadowing; Montag looks at the
"ventilator grille in the hall and suddenly rememberd that something lay hidden behind the grille, something that seemed to peer down at him now."
This foreshadowing lets the reader know that there is a deeper side to Montag, something not quite so straightforward, something that hints that he is not happy, and seeking for answers. The next way that Bradbury conveys a different layer is through figurative language. When he realizes that he isn't happy, Bradbury says Montag
"felt his smile slide away, melt, fold over and down on itself like a tallow skin, like the stuff of a fantastic candle burning too long and now collapsing and now blown out."
This simile, comparing Montag's happiness melting and being snuffed out like a candle, lets us see Montag's misery, as he does, for the first time. This adds another layer to his character.
I hope that helps a bit; good luck!