I wrote a question (Filling out an affidavit of personal service) which received a helpful answer. I upvoted it and accepted it.
My question was downvoted but there was no explanatory comment.
Why?
How am I supposed to learn how to post better questions without any specific feedback?
What is not good about the referenced question?
One of the "features" of Stack Exchange is that votes are anonymous, so unless a downvoter chooses to pipe up there is no way to definitively answer your first question. (There are other features that encourage downvoters to offer explanations.)
Ideally downvotes on questions are used (per the button label) to indicate, "This question does not show any research effort; it is unclear or not useful." In practice people can downvote for any reason, including that they just don't like you, are in a bad mood when they read your question, or let their cat play with the mouse while your question was on their screen.
Absent a comment, you might seek guidance regarding poorly-rated questions in chat, or here on Meta.
Regarding your third request, for feedback on that particular question: You're literally asking, "How do I fill out this government form?" Personally, my first response to such a question would be, "Read the instructions, and if they're unclear contact the government agency that published it, or for which you are completing it." (I'm actually having a hard time thinking of a question that shows less research effort.)
