When I ask a question, then obtain a question in response, how do I enter and respond to the question?
To simply put this into an answer: You should use the comment feature to respond to users or to ask for clarification. You can always comment on your own questions and answers. Once you earn 50 reputation, you can comment on anybody's post.
If you want to mention a user in your comment you ping him with
@user, but substitute
user for his name. So if you want to ping me you would type
In the comments you can use the usual markdown you can use in questions/answers (code highlighting, font adjustments etc.), but avoid putting too many important information in there. Sometimes you should edit your own question instead (or of course answer, if you found a solution).