Hello!
Just go to the thread you want to follow and scroll down. There should be an option to bookmark it.
You get to your bookmarks by clicking the 'View bookmarks' link at the top near the logout button.
This way you can keep track of threads without posting in them and you can delete them from your bookmarks at any time if you lose interest in them.
thanks! I am still quite new to this so I am quite confused about some things...