From the first course to the bill, a handful of phrases will carry you through the whole meal:

Spanish	English
La carta, por favor.	The menu, please.
Quería… / Me gustaría…	I'd like…
Para mí, …	For me, …
De primero / De segundo / De postre	As a starter / For the main course / For dessert
Otra, por favor.	Another one, please.
¡Está buenísimo!	It's delicious!
La cuenta, por favor.	The bill, please.
¿Cuánto es?	How much is it?

The waiter is el camarero, the waitress la camarera. Water comes con gas (sparkling) or sin gas (still).