ok if you post in the pictures section there is a tab marked attachments, click it and navigate to the folder the pics are in, then click upload!
if you want to post in other sections you need to get yourself a Photbucket or imageshak account, do a g??gle search for photo hosting. once you have done that, copy the IMG link to your pic and simply paste it into your post.
IMO, I think that getting a photobucket account...www.photobucket.com...So you can also have all your photos at hand in case you have the need to post the picture again or something. Plus its free