Well, when you post a message, go to mode advanced first. Then go down the page and a white button will say manage attachments. Click on it, and it will pop up. Sometimes if you have a popup blocker it could cause trouble but hopefully not.
When's it's popped up, click browse, and then it will pop up a list of your files on your computer. click on the one you want, then say upload, then post.
If it's on the internet, click on the little box with a green mountain on it, above the normal posting box. It will open, then type in the address of the picture, not the site the picture is on, but the picture itself. Then bingo, hopefully it will work.