Most commonly people think of a place where you sit down and are served by a waiter when you are talking about a restaurant, but restaurants can also include casual establishments and fast food restaurants.
A fine dining restaurant offers full table service and the experience should involve good quality ingredients and a high level of service. Often people will dress up when going to a fine dining restaurant.
The most frequented restaurants are the fast food giants, with number one being McDonald's, followed by KFC and Subway.
A casual dining restaurant is a sit down restaurant where the are less formalities and a more easy going atmosphere. You will generally have a waiter come and take you order and deliver your meal to your table.