"For whom" is used to ask about the person or people to whom something belongs or is intended. It is a formal way of asking about the recipient of something.

Here are some examples of "for whom" in a sentence:

"For whom is this letter intended?" (这封信是给谁的？)
"For whom are you buying these flowers?" (你要为谁买这些花？)
"For whom do you work?" (你为谁工作？)

The phrase "for whom" is a conjunction of "for" and "whom," where "for" indicates purpose or intended recipient, and "whom" is the objective form of "who," used to refer to the object of a verb or preposition. The phrase is used as a question to ask about the recipient of something.

In spoken Engpsh, "for whom" is often shortened to just "who" in informal situations. For example:

"Who are you buying these flowers for?" (你要为谁买这些花？)

I hope this helps! Let me know if you have any other questions.