Pizza is a quick and convenient meal. In most cities there are pizza shops that sell by the gram. Look for a sign Pizza al taglio. When ordering, simply point to the display or tell the attendant the type of pizza you would like (e.g. pizza margherita, pizza con patate (french fries), pizza al prosciutto (ham), etc.) and how much ("Vorrei (due fette - two slices) or (due etti - two-tenths of a kilogram) or simply say "di piů - more" or "di meno - less" per favore"). They will slice it, warm it in the oven, fold it in half, and wrap it in paper. Other food shops also sell pizza by the slice. Italians consider this a sort of second class pizza, chosen only when you cannot eat a "real" pizza in a specialized restaurant (Pizzeria). Getting your meal on the run can save money--many sandwich shops charge an additional fee if you want to sit to eat your meal. Remember that in many parts of the country pizzas have a thinner base of bread and less cheese than those found outside Italy. The most authentic, original pizzas is found in Naples - often containing quite a few ingredients.
The traditional, round pizza is found in many restaurants and specialized pizza restaurants (pizzerie). It is rare to find a restaurant that serves pizza at lunchtime, however.