Somebody has just finished drinking his tea, his cup is empty. Can I say "he's drunk all the/his tea"? Or "he has finished his tea"? - Yes. They all mean the same thing. "he's drunk" sounds less polite and more crude, however, since it refers to the physical act rather than his personal situation. Sometimes I read "Are you finished" instead of "Have you finished". For example, a child stopped eating his meal and is playing now. His mother wants to know if he eats up the rest of his meal. She asks: are you finished? I don't understand this question... I'd ask: have you finished eating your meal/porridge? - It is very natural in English to omit the object in this question, if it is obvious what you are talking about. Another question is: - What are you drinking? Is the answer "some tea" incorrect? I'm not sure about "some"... - the normal answer is "tea" - some people say "some tea" and there is nothing wrong with it - it does not change the meaning

All are correct. They're just different ways to say the same things. I think... The connotation (the meaning behind certain words) of "Are you finished" versus "Have you finished" sounds harsher/sharper in my opinion. "Are you finished" sounds slightly more interrogative, like you're questioning somebody. However, that's just what I think. I could be wrong. "Some tea" is a correct answer. You can just say "I'm drinking tea" or "just tea", but these are just alternatives of saying basically the same thing.

In the beginning, It would be "he drank all his tea" or "he has finished his tea" would be OK too. "Has" in the context of that sentence means this is happening now. He just finished his tea now. So, if you want to know that specifically, then you put the "has", otherwise you can just say "he finished his tea" and make it past tense. In the second part, you can use either and it would still be correct. Grammatically, while you are still learning "are you finished with your meal?" should be what you focus on. For the third question, yes, you can say "some tea" "Some" is always referring to something none specific, so it can be used to describe a lot. You wouldn't say "the tea" because that is referring to something specific and nobody understands what specific tea that is. Now, if you said "the tea that I bought a few days ago" that would make sense.