There are no “pages” to any of the threads here. Every thread runs all the way from the original post at the top of the thread all the way down to the most recent post at the bottom. At the bottom, just beyond the most recent post, you’ll see a “Reply” button. That’s the button you’re after, in order to post to that thread.
Something like this:
There’s also a “Sandbox” thread somewhere, where you can just post any old nonsense and press all the buttons, to have a practice: