The quick version is that ‘civilization,’ by which Freud means any social unit above the family, is intimately tied in to the repression of various instinctual drives. He finally arrives at what I take to be the crucial formula near the end of the book (pg 97, in my edition). Our instincts may be divided into libidinal and aggressive types, that is, the love and death drives, Eros and Thanatos (though Freud doesn’t use the name in this text). Entrance into society, civilization in the broadest sense, is the repression of these drives. Libidinal drives survive repression in the form of symptoms; the repression of aggressive instincts, the death drive, on the other hand, results in guilt. Man (that is, humans, but especially men) in civilization are thus marked by neurotic symptoms, and also a sense of all-pervasive guilt, which is sometimes plainly manifest, but more often disguised as a generalized malaise, ‘discontent,’ or, in the german title, das Unbehagen.
The above is a simplification, though I hope not too much of a distortion. All I want to notice about this now is what a good teaching text it would be. Enough Freud for a class that isn’t specifically about psychoanalysis; a fascinating document of the moment just before the second world war; and of course the way in to Marcuse and a whole slew of 50s and 60s radical theory. It’s short, but I think you could trim the first two sections without loosing terribly much, so that it’s a total of about 70 pages.