Chapter 2 starts out with a comparison between the Encyclopedia Galactica, which gives a very dry definition of alcohol; and the Hitchhiker's Guide, which gives the recipe for the best alcoholic drink ever: the Pan Galactic Gargle Blaster.
Drinking a Pan Galactic Gargle Blaster is like "having your brains smashed out by a slice of lemon wrapped round a large gold brick" (3). Hitchhiker's Guide kindly supplies this recipe, which may be why it is such a popular book.
Ford orders a huge amount of beer, which is how they do it over there in England. He explains to Arthur that they'll need the beer as "muscle relaxant," a line we've never used before but really ought to try.
Ford explains—and you should get used to Ford explaining things to Arthur—that he's an alien from Betelgeuse and the world is about to end. Just your average English pub talk.