There are several ways to ask for what you want in a restaurant :

May I have
e.g. May I have the special.

Can I have
e.g. Can I have the starter.

I’d like (I would like)
e.g. I’d like a chocolate cake.

I want
e.g. I want to speak to the chef.

Starter (in UK), Appetizer (in USA) = First course of the meal.
Main course (in UK), Entrée (in USA) = Principal part of the meal.
Dessert or Pudding (in UK), Dessert (in USA) = Final part of the meal.

Fact !
To leave a « tip » (when you leave extra money at the end of a meal).
In UK, the tip usually equals 10% of the total bill, but in the USA it is 20% !