Alex+Could you explain to me why "take" and "bring" shouldn't be used?
I think your teacher is saying that it's not polite to use too many imperatives, like
Bring me a steak!
Can/Could you (please) bring me another bottle of water? does not seem impolite to me, however -- although you might say I'd like another bottle of water, please.
I'll take the steak does not seem idiomatic to me. I'll get the steak (said to a waiter) also seems unidiomatic.
The more idiomatic ones are:
I'll have the steak, please.
I'd like the steak, please.
CJ