In the US, people prefer waiting for a table to sitting with people they don't know. This means a hostess may not seat a small group until a small table is available, even if a large one is. If you are sitting at a table with people you don't know, it is impolite to light up a cigarette without asking if it will disturb them.
At American restaurants and coffee shops you are usually served tap water before you order. You may find the bread and butter is free, and if you order coffee, you may get a free refill.
Most cities and towns have no rules about opening and closing time for stores or restaurants, though they usually do make rules for bars. Especially in large cities, stores may be open 24 hours a day.
Serving in restaurants is often large, too large for many people. If you can't finish your meal but would like to enjoy the food later, ask your waitress or waiter for a "doggie bag". It may have a picture of a dog on it, but everybody knows you're taking the food for yourself.
Supper and dinner are both words for the evening meal. Some people have "Sunday dinner". This is an especially big noon meal.
Tips are not usually added to the check. They are not included in the price of the meal, either. A tip of about 15% is expected and you should leave it on the table when you leave. In some restaurants, a check is brought on a plate and you put your money there. Then the waiter or waitress brings you your change.
