Restaurant servers attend to guests at dining establishments, serving them food and beverages. They seat customers, inform them about specials, and answer questions about the menu. They take their orders and deliver the meals to their tables. Very much like waiters, which is the less fancy term for restaurant servers.
Being polite and patient is essential in any profession dealing with customers, and this applies to restaurant servers just the same. They communicate with kitchen staff as well, which is no less of a feat, and contribute to keeping the establishment clean and safe. Taking payment and dealing with customer complaints is also their duty.
A high school diploma will suffice to get you started on the job. Being energetic and positive, thriving in a teamwork atmosphere, and performing well under pressure will be what really matters. You will have to be fast and on your feet during your entire shift, though, so physical stamina is also essential.