In the yellow band above is a link called "File Upload." Follow the instructions. Make sure you have no punctuation in your file names, and that they are not too large, or they will be rejected. Then, if you are successful, the url appears below the picture on the successful upload page. Copy it into the "Opional Image URL" space when you post (make sure you replace the "http://" that is already there. Then, I would always preview your post to see if everything is going to look right and you are ready to post. The other option is to use an existing url if the picture is located on another web-site (such as photobucket, etc). Finally, you can include the picture, or even multiples by posting the url between brackets with "pic" and "/pic" in them. See the formatting link above if I am being confusing.
Have fun.
Michael Siskin