I belong to more than a half dozen forums. This is the only one I have ever seen that does not allow attachments.
There are several tutorials on this site, that show you how to upload attachments.
This is the pictorial version:
Click the "Manage Attachments" button.
Click the "Choose file" buttons to select your photos (or other files).
Then, click upload, and close the window when finished.
If you want to have photos appear in your post, click the new links above "Manage Attachments". Copy the URL, and past it between the IMG tags, like any other photo.
That little button has been staring you in the face.
(You can only upload 3 attachments per post.)