hm i'll try to explain.
think of your picture as information. you need to upload this info/picture to the internet to be stored somewhere, where it can be publicly accessed. you can store it for free at places like
www.flickr.com or
www.photobucket.com. you need to sign up for a free account with a place to store your photo. then, of course, upload your photo there. your photo will have an "url" a location where it can be accessed. the url of this website is
www.socialphobiaworld.com, that's all an url is, an address. your image will have an url. then once you have uploaded your picture somewhere (and therefore has an url) you can post it here by posting the url inbetween the img and /img tags much like you did in your original post, above, except instead of it saying
http://image_url, you will replace that with your actual image url. hope this makes sense!