I could be wrong--but I believe the difference between 'bookmarking' and 'subscribing' to a thread would be that if you subscribe to it, you get active notifications that there's new activity in that thread, whereas bookmarking it just catalogues it in a list for you to revisit when you want.
You can find both your bookmarked and subscribed threads on the main 'community' page, where you'll see it listed before all the forum threads--alongside the 'recent posts' option and such!
Viewing post in "bookmarking" vs. "subscribing" a thread/post?
Thanks, so far I've mainly stick to subscribing and using the bell for noticing new posts or threads there & I've also set preferences of (no) additional mails if new content getting shared, so you guess that "subscribing" describes news when notifications and "bookmarking" just as listing but no info which posts being new, just the titles summarized there?
Edit: just noticed it. So far I've just used that part for browsing through all posts/threads or finding interesting titles than reading the top line that refers to bookmark/subscribe.