A note on this. If you click bottom left "Post Quick Reply" then that's one and done. If you get part way through and all of a sudden you want to do more stuff like bold or add a link or picture you can click on the "Reply" button upper right. It won't erase what you've done it will just open the regular posting window with all the bells and whistles available along with what you've already written.
Also if you are at the top of a regular page there is a Reply button to the right of the thread name and that will take you to the full posting window also.