At the table
Coffee, and when to order what
The rules are real, they are not written down anywhere, and nobody will correct you.
Italian coffee has a small vocabulary and a strong grammar. Nobody will tell you when you get it wrong, which is precisely why it is worth knowing.
The words
Caffè. An espresso. If you ask for a coffee, this is what arrives, and it is what the word means. There is no other default.
Caffè macchiato. An espresso "stained" with a little hot milk. Available and ordered at any hour.
Cappuccino. Espresso with steamed milk, drunk in the morning, with or instead of breakfast.
Latte macchiato. Hot milk stained with coffee. Mostly what children drink. Asking for a "latte" will get you a glass of milk, because that is what the word means.
Caffè lungo. The same amount of coffee pulled with more water. Caffè ristretto is the opposite, and it is what a lot of Italians actually drink.
Caffè corretto. Espresso "corrected" with a splash of grappa or sambuca. More common than you would expect, and not only in the evening.
Marocchino, caffè shakerato, caffè d'orzo. Regional and seasonal; ask.
The rules that are not written down
Milky coffee is mostly a morning habit. Cappuccino goes with breakfast, and the reasoning behind it is digestive rather than ceremonial: milk is thought to sit heavily on a full stomach. Treat it as a strong default and not a rule. Plenty of Italians have a cappuccino at four in the afternoon and nobody thinks anything of it. The one case that genuinely reads as foreign is ordering one immediately after a full meal, and even then the response is closer to mild surprise than to disapproval.
After lunch or dinner, it is an espresso. Small, quick, taken standing or in two mouthfuls at the table.
Coffee comes after dessert, not with it. If you want it alongside, say so, and expect a brief hesitation.
Never with the meal. Coffee closes a meal, it does not accompany one.
At the bar
Most coffee in Italy is drunk standing at a counter, in about ninety seconds, often as part of a conversation with the person making it.
In many bars you pay at the till first, take the receipt to the counter, and put it down where the barista can see it. In others you order and pay afterwards. Watch what the person in front of you does.
Sitting at a table often costs more than standing at the bar, and where it does, the two prices are displayed. That is a legal requirement rather than a local custom, so the information is always somewhere on the wall.
A glass of water usually comes with the espresso without being asked for. It is meant to be drunk before, to clear the palate, not after.