You pay for it, so you might as well know what it does, right?
While trolling through the Government Printing Office's offerings, I found this handy manual on the federal government.
The manual covers all the branches and agencies, as well as quasi-official outfits like the Smithsonian. First surprise? The legislative branch includes the U.S. Botanic Garden.
Alas, there's also plenty to bore you to tears.