Are you on a mobile device? As far as posting goes, if you have a wide enough screen you see a two-pane view with text entry on the left and preview on the right (though you can disable the preview pane), and on the right are a Discard and Submit button. On a narrow screen there's no preview, and above the formatting tools is sort of a title bar - the right-pointing arrow at the right end of the title bar is the Submit button. (I didn't pay attention to it, but I presume there must be a discard button on the left.)
You can also hide the reply field (to view something else, like a message you are replying to) by tapping the orange circle, then come back to it by tapping the circle again.