As surely everyone knows, the cafe is a Parisian institution. Parisians use them as combination club/tavern/snack bars, almost as extensions of their living rooms. They're spots where you can sit alone reading your newspaper, doing your homework, or writing your memoirs; meet a friend or lover; nibble at a hard-boiled egg; or drink yourself into oblivion. At cafes you meet your dates to go on to a show or to stay and talk. Above all, cafes are for people-watching.
Their single common denominator is the encouragement of leisurely sitting. Regardless of whether you have one small coffee or the house's most expensive cognac, nobody will badger, pressure, or hurry you. If you wish to sit there until the place closes, that's your affair. Cafes keep flexible hours depending on the season, the traffic, and the part of town they're in. Nearly all stay open until 1 or 2am, and a few are open all night.
Coffee, of course, is the chief drink. It comes black in a small cup, unless you specifically order it au lait (with milk). Tea (thé, pronounced tay) is also fairly popular but is generally not of a high quality. If you prefer beer, we advise you to pay a bit more for the imported German, Dutch, or Danish brands, which are much better than the local brew. If you insist on a French beer, at least order it á pression (draft), which is superior. There's also a vast variety of fruit drinks, as well as Coca-Cola, which can be rather expensive. French chocolate drinks -- either hot or iced -- are absolutely superb and on par with the finest Dutch brands. They're made from ground chocolate, not a chemical compound.
Now just a few words on cafe etiquette: You don't pay when you get your order -- only when you intend to leave. Payment indicates you've had all you want. Service compris means the tip is included in your bill, so it isn't necessary to tip extra; still, most people leave an extra euro or so. You'll hear the locals call for the "garçon," but as a foreigner it would be more polite to say "monsieur." All waitresses, on the other hand, are addressed as "mademoiselle," regardless of age or marital status. In the smaller cafes, you may have to share your table. In that case, even if you haven't exchanged a word with your table companion, when you leave it's customary to bid him or her au revoir.
You'll pay substantially less in a cafe if you stand at the counter rather than sit at a table, because there's no service charge.