Summarize this article in one sentence.
If you see a number (1, 2, etc.) on the envelope, there are that many unread questions in your inbox. If there is no number, you don’t have any questions to answer (yet!). You’ll see a list of every question you’ve been asked since enabling the Ask feature. If you have a new question, it will appear at the top of the list. Type your response in the text field that appears below. To respond to the user privately, click “Answer Privately” when you’re ready to send the message. If you want the response to be posted to your blog as a public post, click “Post.”  If the question was asked anonymously, you can only respond publicly. Anyone will be able to reblog your public responses, just as they would your regular posts. If you don’t want your responses reblogged, respond to your questions privately.

Summary:
Look at the envelope icon at the top right corner of the dashboard. Click the envelope. Click the pencil icon at the bottom right corner of the question. Decide whether or not to make your response public.