To upload a photo in a forum post, just click on "POST REPLY" (bottom left of page)
Click on Upload attachment; click Choose File and navigate to the file on your computer. Select the file and click "OPEN" (bottom right of screen), then click on "add the file".
Place your cursor in the text box where you want the photo to appear and click on "Place inline".
When you've finished with your post, click on Preview (if necessary) then click on Submit for it to become visible on the forum.
You can load up to 3 photos, and they will load quicker if you reduce the file size of the photos before you select them.
Hope that helps.