If you have the picture you want on line at another site you can link to it. The "image url" is where you insert the link (just delete the "image url" within the bracket and insert the url of the link), and the "alt text" is where you can put whatever word you want to indicate the link, e.g. "picture" or "here". Depending on where your picture is, it may hot link and then you would be able to view it right in your post, but otherwise people will be able to click on it and see your picture. Alternatively, if you want to upload a file from your computer you would click on the upload icon. My late, wonderful, Perry with his favourite toy....