This is supposed to contain useful information on how to reply to specific posts and how to see the thread. To be honest, so far I’ve only been able to reply to something specific once, by accident. So I haven’t yet figured this out, but here it is :).
It looks like it is possible to respond to any of the posts/comments at any time, and, if one is replying to what is not the latest comment, then a link to it will appear in the top right corner of the new post. Otherwise there will be no such link, since the new post responds to the latest previous post (which is located right above it). If you click on that link, the post to which the new post is replying will appear.