be sure it is like you want it, then hit post.
Another thing to do is if you are replying to another post highlight the content of the subject box (the Re: repeat of the the text of the post you are responding to) and delete it and start your reply there.
If your reply fits in the box it will post with the automatic NM for no message and if it runs longer than the subject box it will continue over into the Text box.
There is a tiny limit on size when posting pics from your computer files. Post from somewhere that gives your pic URL descriptions and add left arrow img space src= on the front of the URL and the right arrow at the end. The only space is between the img and the src. Go to the next line down and repeat as necessary. You will need to put *PIC* or *PICS* in the Subject line of you do it that way.
If you are only posting one pic just put the URL in the Optional Image box. If you do it this way the *PIC* note is automatically put in the subject line for you. Using he Optional Link URL and Link Title boxes will also put a note *LINK* in the subject line for you. The link will be in blue at the foot of your post.