Bradbury develops the theme of censorship through his protagonist, Montag, whose views on censorship evolve across the course of the novel.
In the dystopian society Bradbury envisages, reading and owning books is illegal. As the novel opens, Montag revels in his work as a fireman, a professional who burns books for a living. He both enjoys and is proud of his work.
Meeting Clarisse, however, starts Montag on a path of questioning if he is fulfilled--and deciding he is not. Compounding this, he is shaken by Mildred's suicide attempt and the suicide of woman who dies rather than be without her books. At this point, Montag moves from an unthinking acceptance of censorship to actually taking a book from the woman's house. He goes from pride in his job to not wanting to go back to work.
As he grows closer to the former Professor Faber, Montag comes to actively hunger for the substantial knowledge to be found in books. He begins to oppose censorship and book burnings. From an obedient fireman, he becomes a political subversive who wants to undermine the current system. He begins to gather books and hide them in his house. He even tries to share reading with Mildred. He evolves from being terrified and ashamed of his interest in books to embracing them.
In a final step in his evolution, Montag realizes that it is not books themselves, but their content, that is valuable. He moves from not wanting books censored to a broader vision of not wanting ideas and information in any form censored.
Opening his eyes and learning from his experience, Montag travels a long way from his unquestioning acceptance of censorship to a complete rejection of it.