Speech/Quote button to quote the post you’re replying to.
To quote a post you first need to press the reply button then the speech/quote button.
Alternatively you can select some of the post your replying to and then press the reply button.
Preview button to preview your post on a mobile.
The preview button will change to an edit icon (looks like a pencil) when in preview mode so to get back to editing your post press the edit icon.
edit: updated image to show the hamburger menu that toggles the format menu on/off.