Although you find the word “please” in the expression, and you consider it as a request, the main idea is a command ("Have a drink", "Wash the dishes", and "Try the cookies"). So you know now that the word “please” makes a command into a request.
In this case, actually the guests are asked to drink. This is what we call an imperative sentence: the sentence expresses a command. In real situation, of course we listen to command or we read commands.
It doesn't matter whether it is spoken or written.
We often find such label in many places. Traffic signs are the real examples that have the same patterns. Here they are:
Do you understand the labels? How if you don’t? Do they matter to you or not? Allright, now how about taking a review of the second label. Look at second sign or label, what will happen if a driver turns right and do exactly something he must not do?
Actually labels that instruct someone to do or not to do something can be easily understood with pictures addition, right?! We also have pictures to understand the labels of instruction (imperative)
Click and drag one of the expressions to match with the right pictures !