These four training films for 1940 census enumerators will give you a pretty good idea of what information we'll be getting, an understanding of what some of the terms actually mean, and an occasional guffaw. Grab your beverage of choice and begin with:
Introduction to the 1940 Census (3:19)
Aw, go ahead, you might as well watch The Three Stooges in No Census, No Feeling... I mean, since the link is right up there and all... and it is about the census... and it's colorized! ... heh, you already did, didn't ya?