Hi Jill and welcome to our boards!
Dining reservations are definitely essential for the more popular restaurants on the island. "The Cliff", in particular, is very popular and although they do accept "walk-in" diners it is recommended to book in advance to avoid disappointment.
Booking in advance also has the added advantage of your being able to request a table with nice views more successfully.
Your best bet is to speak to your hotel receptionist or your holiday rep and ask them for advise, or look up the restaurant's details either on the internet or whilst in Barbados in the local phone book and calling them.
Enjoy Barbados and please share your dining experience here on the boards.
Mark
