Hi,
If you mean your profile picture, click the "my profile" tab at the top of the page, you will see a
row of blue buttons, click on "appearance" button and you will see
another button to upload your own photo.
If you mean adding pictures to forum posts, upload your picture to a site like tinypic.com (lots of other choices). You will then have access to a direct link for the photo, something like http:/.../your picture.jpg that you can then copy/paste. When posting, click the "insert media" icon, where you can insert your picture by pasting your picture's direct link.
-Keith