Some people may insist on ordering an "expresso," but what they really want is an "espresso," which in Italy is a special thing.
Drunk between 11 am and the late night hours, espresso, also known as caffe' is strong coffee made by using high quality beans that are ground into a fine-medium coarseness and measured out in the exact amount.
The coffee-to-water ratio is what determines how strong the espresso will be. Less water is used for stronger espresso and more water for a less intense flavor.
The grounds need to be tamped or pressed with about 30 lbs of pressure to make them into a compact pod. Some of the more contemporary automatic or super-automatic espresso machine press the grounds for you. The press is critical for making a good cup of espresso. The compressed grounds should be smooth and even, and excess grounds should be brushed away.
Pressurized water in the espresso machine is then pushed through the grounds for about 30 seconds for 1-3oz of espresso. Espresso will start to fill the cup (tazzina), and towards the end of the brewing time a light brown, creamy foam (crema) will form on the top of the espresso. When the foam lightens, the espresso is ready to drink down quickly. A sipping coffee it is not.
One thing to keep in mind: never order a cappuccino after 11 am in any Italian bar; that is a dead giveaway that you are a foreigner and do not understand the customs surrounding coffee in Italy. Cappuccino is a morning drink and always will be.
Here are some other types of coffee combinations with which to familiarize yourself. Just please, whatever you do, don't order an "expresso."
Doppio : a double espresso.
Ristretto: More concentrated than a regular espresso made with less water.
Lungo or Caffe' Americano: made with more water
Macchiato: Espresso that is "marked" with a dollop of steamed milk on top.
Corretto: Espresso "corrected" with grappa, cognac or sambuca.
Cappuccino: Espresso with foamed milk and containing equal parts espresso, steamed milk and foamed milk.
Cappuccino scuro: Cappuccino prepared with less milk
Cappuccino chiaro: Cappuccino prepared with more milk (but less than a caffe latte) and is lighter in color.
Caffe' latte: Espresso made with more milk than a cappuccino but only a small amount of foam. In Italy it is usually a breakfast drink.
Latte macchiato: Steamed milk that is "marked" with a shot of espresso coffee.