One of the primary problems that waiters, especially in fine dining restaurants, face is customers ordering items without understanding what they are, and then sending them back, or even becoming angry that they weren’t informed of what they were actually ordering. For the waiter, it is not always clear when to explain something and when not to explain it. Sometimes, a guest will let you know that they are unsure. They may not tell you verbally, but they will show you in other ways. If you are paying attention and ‘reading the table’ you may pick up on it.
Other times, a guest may seem to know exactly what they want, but then turn out to be ordering blind. Menus try to explain what dishes are, but there is limited space, and some menus may fall short or even fail to explain the dishes at all.

It is the waitstaff’s job, after all, to know the menu and be able to explain it. This doesn’t mean that knowing how much you should explain is always clear. You don’t want to assume ignorance and embarrass a guest, or worse yet, make them angry.
When someone orders the steak tartare, and you’re not sure that they realize this is raw beef, should you ask them? What if they order a type of cold soup? Should you let them know? And if so, how do you impart this information without appearing to be pompous?
The best answer I have seen comes from the Culinary Institute of America’s Guide to Remarkable Service. It is normal to repeat an order back to a guest.
When you need to gently and subtly find out if a guest ordered something they may not actually want, you can simply rephrase the order. “You would like the chilled soup and…”
For the example of steak tartare, you might try “You would like the raw minced (or chopped, etc. depending on how the steak is prepared) beef seasoned with…”
Those with advanced food knowledge will know what a dish is by its name. If they don’t, it can be awkward. You have to find a way to inform them without necessarily speaking down to them or seeming to be patronizing — unless you’re a waiter in a high-end French restaurant on a sitcom, that is — but sometimes menus fail to describe pertinent aspects of original dishes.
I once ordered a chicken dish based on the menu description. It came to me ice-cold. The plate, the strips of skinless poached chicken breast, and everything else. I personally do not like cold food. I especially do not like a plate that was prepared in the morning and placed in a refrigerator for hours to await my order.
Despite this, there was nothing on the menu to indicate that this dish was chilled. Some dishes have certain components chilled, while others are warm. Few would expect an ice-cold plate for the entree. In this instance, I would have welcomed a little heads-up from our waiter.
I would advise any waiter to be aware of shortfalls in menu information and simply inform the diner when something is unusual about the dish, unfamiliar, or exotic.
Other times, when it is hard to be sure what to do, use the method described above, and rephrase the order to describe the dishes, but don’t be too obvious about it. This method is often used, and there is probably not a better way.