You need to put the URL of the image you would like to post within [ img] and [ /img] tags (without putting the spaces in the tags; that breaks them).
When you're in the process of posting, you can click the
button or type the tags in manually.
If you would like to post a picture from another website, right-click on the image and select "copy image address," and paste it between the tags.
If you would like to post a picture of your own, then you will need to upload it to an image host, such as
imgur. Once you have upload the image, it will typically give you different links for different things, as seen on this image that I just uploaded:
http://imgur.com/2HgBcWc. You could either right-click on this image, copy the address, and post it between image tags, or copy the "BBCode (message boards & forums)" link and paste it, as it already has the tags.
