Great question Aaron! The LessWrong team wrote a good description of it that I’m going to steal:

• Ask a Question. In your user menu (in the upper right corner of the screen) there is now an option for questions to ask a question, which will create a post with the question-flag. For now, it'll appear normally in lists of recent posts (including the home page, daily and your personal profile)
• Answer a Question. This is similar to a comment, but the formatting is different to highlight that this is meant to have a different feel than commenting. Answers should aspire to resolve a question as accurately and thoroughly as possible, such that if you just read the question-followed-by-single-answer you'd have a pretty complete understanding of the issue.
• Comment on an Answer. By default, only the top 3 comments will be displayed, but if you want to dig into the discussion of a given answer you can expand them.
• Comment on a Question. You can comment on an overall question, without answering. This is for if you're still trying to understand the question, or you think it's making a conceptual mistake, or you just have some thoughts that don't neatly fall into the "answer" format.
• Specialized Table of Contents. Questions with at least one answer automatically have a Table of Contents, even if there are no headings, to help users orient on a fairly complicated page.

(From: https://www.lesswrong.com/posts/mrGeJ4Wt66PxN9RQh/lw-update-2018-12-06-table-of-contents-and-q-and-a)