To have the picture shown you use [img]pictureurl[/img], but if you just want to link it, and not show the picture, you use [url=puturlhere]name the link[/url]. :3
If you want to link a picture in the description you get the picture URL and you use the code [img]insertpictureURLhere[/img]. (Note: Links are not allowed in the actual content of the story, like the chapters.)