What leads Malcolm X to the idea that he ought to study a dictionary?

Malcolm X is in prison and realizes he can't read or write very well. He can't write letters easily to people outside of prison or read them well either. He doesn't understand the books in the prison library, and he has a lot of time on his hands with nothing to do. Therefore, he decides to improve his reading and writing by copying out the entire dictionary. He begins with aardvark and moves on through the letters.
Copying out the entire dictionary does greatly improve his ability to read and write. With his improved reading skills, he begins to read the books in the prison library, and they open up new worlds for him. As he puts it, even though he is in prison, because of books he feels free.