In the US, a fee is a charge for something specific, added to the check. For example, some restaurants will add a fee if you bring your own bottle of wine to drink at dinner (typically called a corkage fee). A tip is an amount of money left by the customer for the waiter/waitress. In theory, it is a reward for good service. At most restaurants where you sit down at a table and are served by a waiter, you should leave 15-20% tip for the waiter. Technically this is optional. However, most restaurants do not pay their servers well, and waiters often depend on their tips to make a living.