just copy and paste the web page address of the photo you want to use into the box into and click ok it will automaticaly add the image tags to the beggining and end of the address.in the post it'll look something like this...(IMG)http://www.webpage/photo.jpg(IMG) exept it'll use square brackets around the IMG tags,if the addy is right,when you submit the post it should show the picture where the image tag was.
another thing you might wanna try is a website called photobucket,the nice thing about it is that when you upload a photo on the site,it automaticaly gives you an image tag that you can copy and paste under the photos you upload.