"Why can't I say it like this? Here's a situation in a restaurant. The waiter has given me poor service, so I want to speak to the head waiter." It's polite to put your demands in question form, as requests with "please" at the end. Perhaps this shows you still have some self-control and manners, even when you're angry. A direct statement sounds rude, and you'll get even less help! I'd sooner say, "Could I speak to the manager, please?" I'm not sure how old your textbook is, or who compiled it, but I agree with MK7's comments about it. "I want to look the head waiter" is a mis-translation. "Look" doesn't take an object, and the closest form is "look at"... which means you can see the head waiter, but not speak to him/her! "See" suggests that you'll have a conversation.

The verb look should instead be the verb see. I want to see the head waiter (please). Fairly blunt.. I'd like to see the head waiter (please). More polite. In real life, you'd actually say that you want to see the manager or, in a high end restaurant that has one, the maitre d'. I want to see the manager (please). I'd like to see the manager (please). The foregoing is more likely than what your textbook recommends - "Would you call (over) the head waiter, please" - which is stuffy and makes you sound like you're living in Edwardian England.