If I want to ask a question in a polite way, how should I ask?
In the same way, there may be other important grammatical rules. Could you please explain me?
These sentences come in two parts. Let's look at each part, first as a statement and then as a question. Note that the word order is inverted in the question.
You could tell me... statement, not inverted
Could you tell me... question, inverted
Where you are from. statement, not inverted
Where are you from? question, inverted.
When you phrase a polite question, the polite bit is grammatically the question (so it's inverted), and what you want to ask is simply a statement (so it's not inverted).
So, in the correct versions of your two questions, the word order of what you want to ask (the highlighted bit) is not inverted.
- May I ask you what your name is?
- Could you tell me where you are from?
The simple way to ask someone's name is to say, "What is your name?"
If you are concerned that a question -- any question -- is abrupt or potentially rude, you can soften it by saying, "Excuse me, but ..." or "Would you please tell me ..." or "Would you mind telling me ...".
In your examples, "May I ask you what your name is?" is valid. "May I ask you what's your name?" is awkward; a fluent speaker wouldn't say that. Well, someone might say that in informal speech, but you wouldn't write it or use it in formal speech. Use of contractions gets tricky some times. Usually you can only use a contraction when it can be expanded in place. Here, you wouldn't say, "May I ask you what is your name?" Though we break this rule for questions sometimes. It's okay to say, "Don't you like apricots?", meaning, "Do you not like apricots?" But no fluent speaker would say, "Do not you like apricots?".
You can ask, "Could you tell me where you are from?" Note "where you are" not "where are you". "Could you tell me where you're from?" is fine, because the contraction expands in place.
Perhaps your uncertainty is with the wording of "indirect" questions like this.
"Where are you from?"
"Can you tell me where you are from?"
Note the order of the subject and verb changes, from "are you" to "you are". In general in English, a statement is written subject - verb - object. Questions that you "is" or "are" are generally is/are - subject - verb or is/are - subject - adjective. Like "Is Bob going?" or "Is Bob tall?" Questions that use an interrogative word like who, how, why, what, or where are generally interrogative - is/are - subject - object or interrogative is/are - subject - infintive verb. Like, "Who are Bob's friends?" or "Where is Bob going?" With do/does it become interrogative - do/does - subject - verb. Like, "What does Bob eat?" or "How does Bob think?"
