A brief answer is that Montag wants to learn to read well enough so that he can understand what he is reading. He might be able to pronounce or "call" words, but he can't read well enough to understand the deeper meanings behind the surface of the words.
Faber simply tells Montag that he can help him, but that won't satisfy him. Montag wants someone to vent to as well. He doesn't completely understand why the burning of books is the law, and eventually becomes a rebel against this system of rules.
Montag was frustrated and hopeless. He turned to Faber who he had remembered from a past encounter. When he went to Faber's home, Faber didn't want to let him in the apartment. Montag assures Faber that he is alone and Faber lets him into the apartment. When he gets inside the apartment Faber notices that Montag is carrying a book. They speak breifly about the book and then Faber asks Montag, "Well-suppose you tell me why you came here?" Montag responds, "I just want someone to hear what I have to say. And maybe if I talk long enough, it'll make sense. And I want you to teach me to understand what I read." (pg. 84)