Guy Montag is a fireman who lives society where books have been banned by a government fearing critical thinking. 451 degrees (Fahrenheit) is the temperature at which paper burns.
The new Fahrenheit 451 in the works is expected to be a better movie and more closely tied to Bradbury's book than this version. The following video is (LOOSELY) based on Ray Bradbury's novel, 'Fahrenheit 451' and not the best interpretation:
The movie is about 1 hour 50 minutes long and might be more interesting than reading the Cliffs Notes version, but don't write your report based on the movie. ;)